Add external-tools.md to the Makefile

Author: matklad

Makefile.in

@@ -160,7 +160,7 @@ clean:
 
 DOCS := index faq config guide manifest build-script pkgid-spec crates-io \
 	environment-variables specifying-dependencies source-replacement \
-	policies machine-readable-output
+	policies external-tools
 DOC_DIR := target/doc
 DOC_OPTS := --markdown-no-toc \
 		--markdown-css stylesheets/normalize.css \

src/doc/external-tools.md

@@ -91,7 +91,7 @@ the `.d` files alongside the artifacts.
 Cargo is designed to be extensible with new subcommands without having to modify
 Cargo itself. This is achieved by translating a cargo invocation of the form
 cargo `(?<command>[^ ]+)` into an invocation of an external tool
-`cargo-${command} that then needs to be present in one of the user's `$PATH`
+`cargo-${command}` that then needs to be present in one of the user's `$PATH`
 directories.
 
 Custom subcommand may use `CARGO` environment variable to call back to

src/doc/header.html

@@ -27,7 +27,9 @@ <h1>CARGO</h1>
                 Docs
                 <span class="arrow"></span>
             </button>
-            <!-- Sync this list with https://github.com/rust-lang/crates.io/blob/master/app/templates/application.hbs -->
+            <!-- Sync this list with
+                 https://github.com/rust-lang/crates.io/blob/master/app/templates/application.hbs
+                 and with Makefile.in in this repository -->
             <ul id="current-user-links" class="dropdown" data-bindattr-503="503">
                 <li><a href='index.html'>Getting Started</a></li>
                 <li><a href='guide.html'>Guide</a></li>