readme update

git-svn-id: https://plugins.svn.wordpress.org/nextgen-facebook/trunk@816075 b8457f37-d9ea-0310-8a92-e5e31aec5664
readme update

git-svn-id: https://plugins.svn.wordpress.org/nextgen-facebook/trunk@816077 b8457f37-d9ea-0310-8a92-e5e31aec5664
improved code for delete_expired_file_cache() method

git-svn-id: https://plugins.svn.wordpress.org/nextgen-facebook/trunk@816078 b8457f37-d9ea-0310-8a92-e5e31aec5664
readme update

git-svn-id: https://plugins.svn.wordpress.org/nextgen-facebook/trunk@816079 b8457f37-d9ea-0310-8a92-e5e31aec5664