edit readme.txt

git-svn-id: https://plugins.svn.wordpress.org/twitter-tweets-button/trunk@1021720 b8457f37-d9ea-0310-8a92-e5e31aec5664
edit readme.txt

git-svn-id: https://plugins.svn.wordpress.org/twitter-tweets-button/trunk@1021723 b8457f37-d9ea-0310-8a92-e5e31aec5664