[release-branch.go1.9] doc: document go1.9

Change-Id: I97075f24319a4b96cbeb9e3ff2e7b2056ff59e32
Reviewed-on: https://go-review.googlesource.com/58651
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-on: https://go-review.googlesource.com/58710
Reviewed-by: Chris Broadfoot <cbro@golang.org>
diff --git a/doc/devel/release.html b/doc/devel/release.html
index e4821ff..8304522 100644
--- a/doc/devel/release.html
+++ b/doc/devel/release.html
@@ -20,7 +20,14 @@
 and Go 1.9 is supported until Go 1.11 is released.
 We fix critical problems, including <a href="/security">critical security problems</a>,
 in supported releases as needed by issuing minor revisions
-(for example, Go 1.8.1, Go 1.8.2, and so on).
+(for example, Go 1.9.1, Go 1.9.2, and so on).
+</p>
+
+<h2 id="go1.9">go1.9 (released 2017/08/24)</h2>
+
+<p>
+Go 1.9 is a major release of Go.
+Read the <a href="/doc/go1.9">Go 1.9 Release Notes</a> for more information.
 </p>
 
 <h2 id="go1.8">go1.8 (released 2017/02/16)</h2>