doc: add important info for would-be go contributors.
Link to the "installing from source" docs instead of the "installing" docs.
Remind would-be hacker to switch to the default branch from the release branch.
R=rsc
CC=golang-dev
https://golang.org/cl/6559043
diff --git a/doc/install-source.html b/doc/install-source.html
index d9f9577..d356cdf 100644
--- a/doc/install-source.html
+++ b/doc/install-source.html
@@ -150,6 +150,18 @@
$ hg clone -u release https://code.google.com/p/go
</pre>
+<h2 id="head">(Optional) Switch to the default branch</h2>
+
+<p>If you intend to modify the go source code, and
+<a href="/doc/contribute.html">contribute your changes</a>
+to the project, then move your repository
+off the release branch, and onto the default (development) branch.
+Otherwise, skip this step.</p>
+
+<pre>
+$ hg update default
+</pre>
+
<h2 id="install">Install Go</h2>
<p>
