add screenshot

git-svn-id: https://plugins.svn.wordpress.org/nextgen-facebook/trunk@746837 b8457f37-d9ea-0310-8a92-e5e31aec5664
add screenshot

git-svn-id: https://plugins.svn.wordpress.org/nextgen-facebook/trunk@746838 b8457f37-d9ea-0310-8a92-e5e31aec5664