doc: document Go 1.4.2

Change-Id: Ia87047cbc720fb03d2f67aec48abe18bce8dbf78
Reviewed-on: https://go-review.googlesource.com/5112Reviewed-by: Russ Cox <rsc@golang.org>

doc/devel/release.html

@@ -26,6 +26,11 @@ go1.4.1 (released 2015/01/15) includes bug fixes to the linker and the <code>log
 See the <a href="https://github.com/golang/go/issues?q=milestone%3AGo1.4.1">Go 1.4.1 milestone on our issue tracker</a> for details.
 </p>
 
+<p>
+go1.4.2 (released 2015/02/17) includes bug fixes to the <code>go</code> command, the compiler and linker, and the <code>runtime</code>, <code>syscall</code>, <code>reflect</code>, and <code>math/big</code> packages.
+See the <a href="https://github.com/golang/go/issues?q=milestone%3AGo1.4.2">Go 1.4.2 milestone on our issue tracker</a> for details.
+</p>
+
 <h2 id="go1.3">go1.3 (released 2014/06/18)</h2>
 
 <p>