[release-branch.go1.7] doc: document go1.7.3 and add note to go1.7.2 that it should not be used

Change-Id: I3dd1513e927733ce5c63928da772cb81760ba869
Reviewed-on: https://go-review.googlesource.com/31442Reviewed-by: Andrew Gerrand <adg@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

doc/devel/release.html

@@ -50,11 +50,17 @@ See the <a href="https://github.com/golang/go/issues?q=milestone%3AGo1.7.1">Go
 </p>
 
 <p>
-go1.7.2 (released 2016/10/17) includes fixes to the compiler, runtime,
+go1.7.2 should not be used. It was tagged but not fully released.
+The release was deferred due to a last minute bug report.
+Use go1.7.3 instead, and refer to the summary of changes below.
+</p>
+
+<p>
+go1.7.3 (released 2016/10/19) includes fixes to the compiler, runtime,
 and the <code>crypto/cipher</code>, <code>crypto/tls</code>,
 <code>net/http</code>, and <code>strings</code> packages.
-See the <a href="https://github.com/golang/go/issues?q=milestone%3AGo1.7.2">Go
-1.7.2 milestone</a> on our issue tracker for details.
+See the <a href="https://github.com/golang/go/issues?q=milestone%3AGo1.7.3">Go
+1.7.3 milestone</a> on our issue tracker for details.
 </p>
 
 <h2 id="go1.6">go1.6 (released 2016/02/17)</h2>