Update Readme File

git-svn-id: https://plugins.svn.wordpress.org/shortcode-button/trunk@872638 b8457f37-d9ea-0310-8a92-e5e31aec5664
Update Readme File

git-svn-id: https://plugins.svn.wordpress.org/shortcode-button/trunk@872641 b8457f37-d9ea-0310-8a92-e5e31aec5664