doc: document r60.2

R=rsc, dsymonds
CC=golang-dev
https://golang.org/cl/5204041

doc/devel/release.html

@@ -104,6 +104,12 @@ a new
 option</a>.
 </p>
 
+<p>
+r60.2
+<a href="http://code.google.com/p/go/source/detail?r=ff19536042ac">fixes</a>
+a memory leak involving maps.
+</p>
+
 <h2 id="r59">r59 (released 2011/08/01)</h2>
 
 <p>