link to flutter from readme

Author: sethladd

README.md

@@ -2,7 +2,7 @@
 
 [![Build Status](https://travis-ci.org/flutter/atom-flutter.svg?branch=master)](https://travis-ci.org/flutter/atom-flutter)
 
-A Flutter development environment for Atom.
+A [Flutter][] development environment for Atom.
 
 ## Features and bugs
 
@@ -14,3 +14,5 @@ Please file feature requests and bugs at the [issue tracker][tracker].
 
 This plugin uses functionality from the
 [dartlang](https://github.com/dart-atom/dartlang) plugin.
+
+[Flutter]: http://flutter.io