Update the README

git-svn-id: https://plugins.svn.wordpress.org/mediacore/trunk@939732 b8457f37-d9ea-0310-8a92-e5e31aec5664
Update the stable tag to 2.4.1

git-svn-id: https://plugins.svn.wordpress.org/mediacore/trunk@939734 b8457f37-d9ea-0310-8a92-e5e31aec5664