added support for wp 3.9 to readme

git-svn-id: https://plugins.svn.wordpress.org/wp-twitter-autopost/trunk@900530 b8457f37-d9ea-0310-8a92-e5e31aec5664
updated readme file upload

git-svn-id: https://plugins.svn.wordpress.org/wp-twitter-autopost/trunk@900531 b8457f37-d9ea-0310-8a92-e5e31aec5664