Add note saying this will be the last release supporting Python2.6

NEWS

@@ -12,6 +12,10 @@
 
   * Fix inconsistent handling of trailing slashes for DictRefsContainer. (#383)
 
+ CHANGES
+
+  * This will be the last release to support Python 2.6.
+
 0.11.2	2015-09-18
 
  IMPROVEMENTS