doc/howto_release.txt: updated

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@71709 15284696-431f-4ddb-bdfa-cd5b030d7da7

doc/howto_release.txt

@@ -232,6 +232,8 @@ Contents
 
 2. Tell others about it:
 
+ * Notify all packagers (MN has email list)
+
  * If release candidate:
     - <grass-announce@lists.osgeo.org>
     - <grass-dev@lists.osgeo.org>