update readme

git-svn-id: https://plugins.svn.wordpress.org/personal-content-recommendations/trunk@908007 b8457f37-d9ea-0310-8a92-e5e31aec5664
update readme

git-svn-id: https://plugins.svn.wordpress.org/personal-content-recommendations/trunk@908009 b8457f37-d9ea-0310-8a92-e5e31aec5664