edited readme

git-svn-id: https://plugins.svn.wordpress.org/custom-content-shortcode/trunk@991592 b8457f37-d9ea-0310-8a92-e5e31aec5664
edited readme

git-svn-id: https://plugins.svn.wordpress.org/custom-content-shortcode/trunk@991594 b8457f37-d9ea-0310-8a92-e5e31aec5664