update readme.txt

git-svn-id: https://plugins.svn.wordpress.org/ddevs-media-gallery/trunk@1022099 b8457f37-d9ea-0310-8a92-e5e31aec5664
update readme.txt

git-svn-id: https://plugins.svn.wordpress.org/ddevs-media-gallery/trunk@1022100 b8457f37-d9ea-0310-8a92-e5e31aec5664