add link to go build dashboard.

break the list into two pieces

R=golang-dev
CC=golang-dev
https://golang.org/cl/196088

doc/devel/index.html

@@ -3,5 +3,8 @@
 <ul>
 <li><a href="roadmap.html">Roadmap</a></li>
 <li><a href="release.html">Release History</a></li>
+<li><a href="http://godashboard.appspot.com">Build and benchmark status</a></li>
+</ul>
+<ul>
 <li><a href="../contribute.html">Contributing code</a></li>
 </ul>