doc: document Go 1.5.3

Change-Id: I9b4b76abfba66ff655aef55b43d9b4721aba604a
Reviewed-on: https://go-review.googlesource.com/18587Reviewed-by: Chris Broadfoot <cbro@golang.org>

doc/devel/release.html

@@ -55,6 +55,13 @@ See the <a href="https://github.com/golang/go/issues?q=milestone%3AGo1.5.2">Go
 1.5.2 milestone</a> on our issue tracker for details.
 </p>
 
+<p>
+go1.5.3 (released 2016/01/13) includes a security fix to the <code>math/big</code> package
+affecting the <code>crypto/tls</code> package.
+See the <a href="https://github.com/golang/go/issues?q=milestone%3AGo1.5.3">Go 1.5.3 milestone on our issue tracker</a>
+and the <a href="https://golang.org/s/go153announce">release announcement</a> for details.
+</p>
+
 <h2 id="go1.4">go1.4 (released 2014/12/10)</h2>
 
 <p>