Update readme for WordPress 3.9

git-svn-id: https://plugins.svn.wordpress.org/wider-admin-menu/trunk@897368 b8457f37-d9ea-0310-8a92-e5e31aec5664
Update readme

git-svn-id: https://plugins.svn.wordpress.org/wider-admin-menu/trunk@897370 b8457f37-d9ea-0310-8a92-e5e31aec5664