update readme file

git-svn-id: https://plugins.svn.wordpress.org/scheduled-posts-calendar/trunk@831530 b8457f37-d9ea-0310-8a92-e5e31aec5664
update readme file

git-svn-id: https://plugins.svn.wordpress.org/scheduled-posts-calendar/trunk@831531 b8457f37-d9ea-0310-8a92-e5e31aec5664