add doc/devel/index.html, linked from nav bar

R=r
CC=golang-dev
https://golang.org/cl/181156

doc/devel/index.html

+<!-- The Go project -->
+
+<ul>
+<li><a href="roadmap.html">Roadmap</a></li>
+<li><a href="release.html">Release History</a></li>
+<li><a href="../contribute.html">Contributing code</a></li>
+</ul>

lib/godoc/godoc.html

@@ -88,17 +88,14 @@
     <li><a href="/doc/go_mem.html">Memory Model</a></li>
     <li><a href="/doc/go_for_cpp_programmers.html">Go for C++ Programmers</a></li>
 
-    <li class="blank">&nbsp;</li>
-    <li class="navhead">How To</li>
-    <li><a href="/doc/install.html">Install Go</a></li>
-    <li><a href="/doc/code.html">Write code</a></li>
-    <li><a href="/doc/contribute.html">Contribute code</a></li>
-
     <li class="blank">&nbsp;</li>
     <li class="navhead">Programming</li>
+    <li><a href="/doc/install.html">How to install Go</a></li>
+    <li><a href="/doc/code.html">How to write code</a></li>
     <li><a href="/cmd">Command documentation</a></li>
     <li><a href="/pkg">Package documentation</a></li>
     <li><a href="/src">Source files</a></li>
+    <li><a href="/doc/devel/">The Go project</a></li>
 
     <li class="blank">&nbsp;</li>
     <li class="navhead">Help</li>