Inline docs (#2602)

* Add English docs to repo

* Update PR template to mention documentation requirement

* Add guide markdown linting

Author: lukastaegert

.github/PULL_REQUEST_TEMPLATE.md

@@ -8,6 +8,7 @@
   Pull Request Requirements:
   * Please include tests to illustrate the problem this PR resolves.
   * Please lint your changes by running `npm run lint` before creating a PR.
+  * Please update the documentation in `/docs` where necessary
 
   Please place an x (no spaces - [x]) in all [ ] that apply.
 -->

docs/00-introduction.md

@@ -0,0 +1,87 @@
+---
+title: Introduction
+---
+
+### Overview
+
+Rollup is a module bundler for JavaScript which compiles small pieces of code into something larger and more complex, such as a library or application. It uses the new standardized format for code modules included in the ES6 revision of JavaScript, instead of previous idiosyncratic solutions such as CommonJS and AMD. ES6 modules let you freely and seamlessly combine the most useful individual functions from your favorite libraries. This will eventually be possible natively, but Rollup lets you do it today.
+
+### Quick start
+
+Install with `npm install --global rollup`. Rollup can be used either through a [command line interface](guide/en#command-line-reference) with an optional configuration file, or else through its [JavaScript API](guide/en#javascript-api). Run `rollup --help` to see the available options and parameters.
+
+> See [rollup-starter-lib](https://github.com/rollup/rollup-starter-lib) and
+[rollup-starter-app](https://github.com/rollup/rollup-starter-app) to see
+example library and application projects using Rollup
+
+These commands assume the entry point to your application is named `main.js`, and that you'd like all imports compiled into a single file named `bundle.js`.
+
+For browsers:
+
+```console
+# compile to a <script> containing a self-executing function ('iife')
+$ rollup main.js --file bundle.js --format iife
+```
+
+For Node.js:
+
+```console
+# compile to a CommonJS module ('cjs')
+$ rollup main.js --file bundle.js --format cjs
+```
+
+For both browsers and Node.js:
+
+```console
+# UMD format requires a bundle name
+$ rollup main.js --file bundle.js --format umd --name "myBundle"
+```
+
+### The Why
+
+Developing software is usually easier if you break your project into smaller separate pieces, since that often removes unexpected interactions and dramatically reduces the complexity of the problems you'll need to solve, and simply writing smaller projects in the first place [isn't necessarily the answer](https://medium.com/@Rich_Harris/small-modules-it-s-not-quite-that-simple-3ca532d65de4). Unfortunately, JavaScript has not historically included this capability as a core feature in the language.
+
+This finally changed with the ES6 revision of JavaScript, which includes a syntax for importing and exporting functions and data so they can be shared between separate scripts. The specification is now fixed, but it is not yet implemented in browsers or Node.js. Rollup allows you to write your code using the new module system, and will then compile it back down to existing supported formats such as CommonJS modules, AMD modules, and IIFE-style scripts. This means that you get to *write future-proof code*, and you also get the tremendous benefits of...
+
+### Tree-Shaking
+
+In addition to enabling the use of ES6 modules, Rollup also statically analyzes the code you are importing, and will exclude anything that isn't actually used. This allows you to build on top of existing tools and modules without adding extra dependencies or bloating the size of your project.
+
+For example, with CommonJS, the *entire tool or library must be imported*.
+
+```js
+// import the entire utils object with CommonJS
+const utils = require( './utils' );
+const query = 'Rollup';
+// use the ajax method of the utils object
+utils.ajax(`https://api.example.com?search=${query}`).then(handleResponse);
+```
+
+But with ES6 modules, instead of importing the whole `utils` object, we can just import the one `ajax` function we need:
+
+```js
+// import the ajax function with an ES6 import statement
+import { ajax } from './utils';
+const query = 'Rollup';
+// call the ajax function
+ajax(`https://api.example.com?search=${query}`).then(handleResponse);
+```
+
+Because Rollup includes the bare minimum, it results in lighter, faster, and less complicated libraries and applications. Since this approach is based on explicit `import` and `export` statements, it is more effective than simply running an automated minifier to detect unused variables in the compiled output code.
+
+
+### Compatibility
+
+#### Importing CommonJS
+
+Rollup can import existing CommonJS modules [through a plugin](https://github.com/rollup/rollup-plugin-commonjs).
+
+#### Publishing ES6 Modules
+
+To make sure your ES6 modules are immediately usable by tools that work with CommonJS such as Node.js and webpack, you can use Rollup to compile to UMD or CommonJS format, and then point to that compiled version with the `main` property in your `package.json` file. If your `package.json` file also has a `module` field, ES6-aware tools like Rollup and [webpack 2+](https://webpack.js.org/) will [import the ES6 module version](https://github.com/rollup/rollup/wiki/pkg.module) directly.
+
+### Links
+
+- step-by-step [tutorial video series](https://code.lengstorf.com/learn-rollup-js/), with accompanying written walkthrough
+- miscellaneous issues in the [wiki](https://github.com/rollup/rollup/wiki)
+

docs/01-command-line-reference.md

@@ -0,0 +1,247 @@
+---
+title: Command Line Interface
+---
+
+Rollup should typically be used from the command line. You can provide an  optional Rollup configuration file to simplify command line usage and enable advanced Rollup functionality.
+
+### Configuration Files
+
+Rollup configuration files are optional, but they are powerful and convenient and thus **recommended**.
+
+A config file is an ES6 module that exports a default object with the desired options. Typically, it is called `rollup.config.js` and sits in the root directory of your project.
+
+Also you can use CJS modules syntax for the config file.
+
+```javascript
+module.exports = {
+  input: 'src/main.js',
+  output: {
+    file: 'bundle.js',
+    format: 'cjs'
+  }
+};
+```
+
+It may be pertinent if you want to use the config file not only from the command line, but also from your custom scripts programmatically.
+
+Consult the [big list of options](guide/en#big-list-of-options) for details on each option you can include in your config file.
+
+```javascript
+// rollup.config.js
+
+export default { // can be an array (for multiple inputs)
+  // core input options
+  input,     // required
+  external,
+  plugins,
+
+  // advanced input options
+  onwarn,
+  perf,
+
+  // danger zone
+  acorn,
+  acornInjectPlugins,
+  treeshake,
+  context,
+  moduleContext,
+
+  // experimental
+  experimentalCodeSplitting,
+  manualChunks,
+  optimizeChunks,
+  chunkGroupingSize,
+
+  output: {  // required (can be an array, for multiple outputs)
+    // core output options
+    format,  // required
+    file,
+    dir,
+    name,
+    globals,
+
+    // advanced output options
+    paths,
+    banner,
+    footer,
+    intro,
+    outro,
+    sourcemap,
+    sourcemapFile,
+    sourcemapPathTransform,
+    interop,
+    extend,
+
+    // danger zone
+    exports,
+    amd,
+    indent,
+    strict,
+    freeze,
+    namespaceToStringTag,
+
+    // experimental
+    entryFileNames,
+    chunkFileNames,
+    assetFileNames
+  },
+
+  watch: {
+    chokidar,
+    include,
+    exclude,
+    clearScreen
+  }
+};
+```
+
+You can export an **array** from your config file to build bundles from several different unrelated inputs at once, even in watch mode. To build different bundles with the same input, you supply an array of output options for each input:
+
+```javascript
+// rollup.config.js (building more than one bundle)
+
+export default [{
+  input: 'main-a.js',
+  output: {
+    file: 'dist/bundle-a.js',
+    format: 'cjs'
+  }
+}, {
+  input: 'main-b.js',
+  output: [
+    {
+      file: 'dist/bundle-b1.js',
+      format: 'cjs'
+    },
+    {
+      file: 'dist/bundle-b2.js',
+      format: 'esm'
+    }
+  ]
+}];
+```
+
+If you want to create your config asynchronously, Rollup can also handle a `Promise` which resolves to an object or an array.
+
+```javascript
+// rollup.config.js
+import fetch from  'node-fetch';
+export default fetch('/some-remote-service-or-file-which-returns-actual-config');
+```
+
+Similarly, you can do this as well:
+
+```javascript
+// rollup.config.js (Promise resolving an array)
+export default Promise.all([
+  fetch('get-config-1'),
+  fetch('get-config-2')
+])
+```
+
+You *must* use a configuration file in order to do any of the following:
+
+- bundle one project into multiple output files
+- use Rollup plugins, such as [rollup-plugin-node-resolve](https://github.com/rollup/rollup-plugin-node-resolve) and [rollup-plugin-commonjs](https://github.com/rollup/rollup-plugin-commonjs) which let you load CommonJS modules from the Node.js ecosystem
+
+To use Rollup with a configuration file, pass the `--config` or `-c` flags.
+
+```console
+# use Rollup with a rollup.config.js file
+$ rollup --config
+
+# alternatively, specify a custom config file location
+$ rollup --config my.config.js
+```
+
+You can also export a function that returns any of the above configuration formats. This function will be passed the current command line arguments so that you can dynamically adapt your configuration to respect e.g. `--silent`. You can even define your own command line options if you prefix them with `config`:
+
+```javascript
+// rollup.config.js
+import defaultConfig from './rollup.default.config.js';
+import debugConfig from './rollup.debug.config.js';
+
+export default commandLineArgs => {
+  if (commandLineArgs.configDebug === true) {
+    return debugConfig;
+  }
+  return defaultConfig;
+}
+```
+
+If you now run `rollup --config --configDebug`, the debug configuration will be used.
+
+
+### Command line flags
+
+Many options have command line equivalents. Any arguments passed here will override the config file, if you're using one. See the [big list of options](guide/en#big-list-of-options) for details.
+
+```text
+-c, --config                Use this config file (if argument is used but value
+                              is unspecified, defaults to rollup.config.js)
+-i, --input                 Input (alternative to <entry file>)
+-o, --file <output>         Output (if absent, prints to stdout)
+-f, --format [esm]          Type of output (amd, cjs, esm, iife, umd)
+-e, --external              Comma-separate list of module IDs to exclude
+-g, --globals               Comma-separate list of `module ID:Global` pairs
+                              Any module IDs defined here are added to external
+-n, --name                  Name for UMD export
+-m, --sourcemap             Generate sourcemap (`-m inline` for inline map)
+--amd.id                    ID for AMD module (default is anonymous)
+--amd.define                Function to use in place of `define`
+--no-strict                 Don't emit a `"use strict";` in the generated modules.
+--no-indent                 Don't indent result
+--environment <values>      Environment variables passed to config file
+--noConflict                Generate a noConflict method for UMD globals
+--no-treeshake              Disable tree-shaking
+--intro                     Content to insert at top of bundle (inside wrapper)
+--outro                     Content to insert at end of bundle (inside wrapper)
+--banner                    Content to insert at top of bundle (outside wrapper)
+--footer                    Content to insert at end of bundle (outside wrapper)
+--no-interop                Do not include interop block
+```
+
+In addition, the following arguments can be used:
+
+#### `-h`/`--help`
+
+Print the help document.
+
+#### `-v`/`--version`
+
+Print the installed version number.
+
+#### `-w`/`--watch`
+
+Rebuild the bundle when its source files change on disk.
+
+#### `--silent`
+
+Don't print warnings to the console.
+
+#### `--environment <values>`
+
+Pass additional settings to the config file via `process.ENV`.
+
+```sh
+rollup -c --environment INCLUDE_DEPS,BUILD:production
+```
+
+will set `process.env.INCLUDE_DEPS === 'true'` and `process.env.BUILD === 'production'`. You can use this option several times. In that case, subsequently set variables will overwrite previous definitions. This enables you for instance to overwrite environment variables in `package.json` scripts:
+
+```json
+// in package.json
+{
+  "scripts": {
+    "build": "rollup -c --environment INCLUDE_DEPS,BUILD:production"
+  }
+}
+```
+
+If you call this script via:
+
+```console
+npm run build -- --environment BUILD:development
+```
+
+then the config file will receive `process.env.INCLUDE_DEPS === 'true'` and `process.env.BUILD === 'development'`.