doc: document go1.8.2 and go1.7.6

Change-Id: I2ed2e8c4890a65288cf3066ebe3c1d9a16fb4c05
Reviewed-on: https://go-review.googlesource.com/43990Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

doc/devel/release.html

@@ -42,6 +42,13 @@ See the <a href="https://github.com/golang/go/issues?q=milestone%3AGo1.8.1">Go
 1.8.1 milestone</a> on our issue tracker for details.
 </p>
 
+<p>
+go1.8.2 (released 2017/05/23) includes a security fix to the
+<code>crypto/elliptic</code> package.
+See the <a href="https://github.com/golang/go/issues?q=milestone%3AGo1.8.2">Go
+1.8.2 milestone</a> on our issue tracker for details.
+</p>
+
 <h2 id="go1.7">go1.7 (released 2016/08/15)</h2>
 
 <p>
@@ -88,6 +95,13 @@ See the <a href="https://github.com/golang/go/issues?q=milestone%3AGo1.7.5">Go
 1.7.5 milestone</a> on our issue tracker for details.
 </p>
 
+<p>
+go1.7.6 (released 2017/05/23) includes the same security fix as Go 1.8.2 and
+was released at the same time.
+See the <a href="https://github.com/golang/go/issues?q=milestone%3AGo1.8.2">Go
+1.8.2 milestone</a> on our issue tracker for details.
+</p>
+
 <h2 id="go1.6">go1.6 (released 2016/02/17)</h2>
 
 <p>