.updating the readme file for 4.0 compatibility

git-svn-id: https://plugins.svn.wordpress.org/wp-colorbox/trunk@981724 b8457f37-d9ea-0310-8a92-e5e31aec5664
.updating readme file to fix tag issues

git-svn-id: https://plugins.svn.wordpress.org/wp-colorbox/trunk@981738 b8457f37-d9ea-0310-8a92-e5e31aec5664