Update readme

git-svn-id: https://plugins.svn.wordpress.org/ml-slider/trunk@1011534 b8457f37-d9ea-0310-8a92-e5e31aec5664
Update version to 3.1.1

git-svn-id: https://plugins.svn.wordpress.org/ml-slider/trunk@1011538 b8457f37-d9ea-0310-8a92-e5e31aec5664