Add some docs

Author: wooorm

lib/index.js

@@ -20,7 +20,7 @@
  * @typedef {Literal & {type: 'comment', value: {stitch: UnistNode}}} Stitch
  *
  * @typedef Options
- * @property {Array.<string>} passThrough
+ * @property {Array.<string>} passThrough List of custom hast node types to pass through (keep) in hast. If the passed through nodes have children, those children are expected to be hast and will be handled
  *
  * @typedef HiddenTokenizer
  * @property {Array.<HiddenLocationTracker>} __mixins Way too simple, but works for us.
@@ -85,9 +85,12 @@ var doctypeToken = 'DOCTYPE_TOKEN'
 var parseOptions = {sourceCodeLocationInfo: true, scriptingEnabled: false}
 
 /**
- * @param {Node} tree
- * @param {VFile} [file]
- * @param {Options} [options]
+ * Given a hast tree and an optional vfile (for positional info), return a new
+ * parsed-again hast tree.
+ *
+ * @param {Node} tree Original hast tree
+ * @param {VFile} [file] Virtual file for positional info
+ * @param {Options} [options] Configuration
  */
 export function raw(tree, file, options) {
   var index = -1