doc: document Go 1.9.7

Change-Id: I10dededb41162a99dbc42792a9d314c6dabddcca
Reviewed-on: https://go-review.googlesource.com/116362Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

doc/devel/release.html

@@ -101,6 +101,15 @@ See the <a href="https://github.com/golang/go/issues?q=milestone%3AGo1.9.6">Go
 1.9.6 milestone</a> on our issue tracker for details.
 </p>
 
+<p>
+go1.9.7 (released 2018/06/05) includes fixes to the go command, and the
+<code>crypto/x509</code>, and <code>strings</code> packages.
+In particular, it adds <a href="https://go.googlesource.com/go/+/d4e21288e444d3ffd30d1a0737f15ea3fc3b8ad9">
+minimal support to the go command for the vgo transition</a>.
+See the <a href="https://github.com/golang/go/issues?q=milestone%3AGo1.9.7">Go
+1.9.7 milestone</a> on our issue tracker for details.
+</p>
+
 
 <h2 id="go1.8">go1.8 (released 2017/02/16)</h2>