readme updates

git-svn-id: https://plugins.svn.wordpress.org/mailchimp-for-wp/trunk@780033 b8457f37-d9ea-0310-8a92-e5e31aec5664
readme

git-svn-id: https://plugins.svn.wordpress.org/mailchimp-for-wp/trunk@780035 b8457f37-d9ea-0310-8a92-e5e31aec5664