Add Dart style guide

* Added Go while I was in there. (@rakyll or @adg might have feedback on the link I used)
* Rewrote things a bit to make the new links fit.
* Copy edited a bit because I couldn't help myself.

README.md

@@ -7,27 +7,31 @@ easier to understand a large codebase when all the code in it is in a
 consistent style.
 
 “Style” covers a lot of ground, from “use camelCase for variable names” to
-“never use global variables” to “never use exceptions.” This project holds the
+“never use global variables” to “never use exceptions.” This project
+([google/styleguide](https://github.com/google/styleguide)) links to the
 style guidelines we use for Google code. If you are modifying a project that
 originated at Google, you may be pointed to this page to see the style guides
 that apply to that project.
 
-Our [C++ Style Guide][cpp], [Objective-C Style Guide][objc], [Java Style
-Guide][java], [Python Style Guide][py], [R Style Guide][r], [Shell Style
-Guide][sh], [HTML/CSS Style Guide][htmlcss], [JavaScript Style Guide][js],
-[AngularJS Style Guide][angular], [Common Lisp Style Guide][cl], and [Vimscript
-Style Guide][vim] are now available. We have also released [cpplint][cpplint],
-a tool to assist with style guide compliance, and [google-c-style.el][emacs],
-an Emacs settings file for Google style.
+This project holds the [C++ Style Guide][cpp], [Objective-C Style Guide][objc],
+[Java Style Guide][java], [Python Style Guide][py], [R Style Guide][r],
+[Shell Style Guide][sh], [HTML/CSS Style Guide][htmlcss],
+[JavaScript Style Guide][js], [AngularJS Style Guide][angular],
+[Common Lisp Style Guide][cl], and [Vimscript Style Guide][vim]. This project
+also contains [cpplint][cpplint], a tool to assist with style guide compliance,
+and [google-c-style.el][emacs], an Emacs settings file for Google style.
 
-If your project requires that you create a new XML document format, our [XML
+If your project requires that you create a new XML document format, the [XML
 Document Format Style Guide][xml] may be helpful. In addition to actual style
 rules, it also contains advice on designing your own vs. adapting an existing
 format, on XML instance document formatting, and on elements vs. attributes.
 
-These style guides are licensed under the CC-By 3.0 License, which encourages
-you to share these documents. See [https://creativecommons.org/licenses/by/3.0/](https://creativecommons.org/licenses/by/3.0/)
-for more details.
+The style guides in this project are licensed under the CC-By 3.0 License,
+which encourages you to share these documents.
+See [https://creativecommons.org/licenses/by/3.0/][ccl] for more details.
+
+The following Google style guides live outside of this project:
+[Go Style][go] and [Effective Dart][dart].
 
 <a rel="license" href="https://creativecommons.org/licenses/by/3.0/"><img alt="Creative Commons License" style="border-width:0" src="https://i.creativecommons.org/l/by/3.0/88x31.png" /></a>
 
@@ -45,3 +49,6 @@ for more details.
 [cpplint]: https://github.com/google/styleguide/tree/gh-pages/cpplint
 [emacs]: https://raw.githubusercontent.com/google/styleguide/gh-pages/google-c-style.el
 [xml]: https://google.github.io/styleguide/xmlstyle.html
+[dart]: https://www.dartlang.org/guides/language/effective-dart
+[go]: https://github.com/golang/go/wiki/Style
+[ccl]: https://creativecommons.org/licenses/by/3.0/