readme update

git-svn-id: https://plugins.svn.wordpress.org/adobe-xmp-for-wp/trunk@812909 b8457f37-d9ea-0310-8a92-e5e31aec5664
readme update

git-svn-id: https://plugins.svn.wordpress.org/adobe-xmp-for-wp/trunk@812913 b8457f37-d9ea-0310-8a92-e5e31aec5664