readme.txt update

git-svn-id: https://plugins.svn.wordpress.org/download-manager/trunk@749253 b8457f37-d9ea-0310-8a92-e5e31aec5664
readme.txt update

git-svn-id: https://plugins.svn.wordpress.org/download-manager/trunk@749254 b8457f37-d9ea-0310-8a92-e5e31aec5664