Fixed some messaging.

git-svn-id: https://plugins.svn.wordpress.org/mailchimp-campaigns/trunk@882978 b8457f37-d9ea-0310-8a92-e5e31aec5664
Fixed README.

git-svn-id: https://plugins.svn.wordpress.org/mailchimp-campaigns/trunk@882979 b8457f37-d9ea-0310-8a92-e5e31aec5664