Update readme

git-svn-id: https://plugins.svn.wordpress.org/admin-category-filter/trunk@845430 b8457f37-d9ea-0310-8a92-e5e31aec5664
Change directory structure

git-svn-id: https://plugins.svn.wordpress.org/admin-category-filter/trunk@845431 b8457f37-d9ea-0310-8a92-e5e31aec5664