Readme.txt updates

git-svn-id: https://plugins.svn.wordpress.org/wp-maintenance-mode/trunk@976700 b8457f37-d9ea-0310-8a92-e5e31aec5664
another readme.txt update

git-svn-id: https://plugins.svn.wordpress.org/wp-maintenance-mode/trunk@976701 b8457f37-d9ea-0310-8a92-e5e31aec5664