remove README.txt

git-svn-id: https://plugins.svn.wordpress.org/campaign-monitor-dashboard/trunk@814824 b8457f37-d9ea-0310-8a92-e5e31aec5664
readme update

git-svn-id: https://plugins.svn.wordpress.org/campaign-monitor-dashboard/trunk@814828 b8457f37-d9ea-0310-8a92-e5e31aec5664