[release-branch.go1.7] doc: add 1.7 to golang.org/project

Change-Id: Ib17f6643efd49e2bca188c4faa505f79832d18b1
Reviewed-on: https://go-review.googlesource.com/27110Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-on: https://go-review.googlesource.com/27112Reviewed-by: Chris Broadfoot <cbro@golang.org>

doc/contrib.html

@@ -34,6 +34,7 @@ We encourage all Go users to subscribe to
 <p>A <a href="/doc/devel/release.html">summary</a> of the changes between Go releases. Notes for the major releases:</p>
 
 <ul>
+	<li><a href="/doc/go1.7">Go 1.7</a> <small>(August 2016)</small></li>
 	<li><a href="/doc/go1.6">Go 1.6</a> <small>(February 2016)</small></li>
 	<li><a href="/doc/go1.5">Go 1.5</a> <small>(August 2015)</small></li>
 	<li><a href="/doc/go1.4">Go 1.4</a> <small>(December 2014)</small></li>