Change Git to git on readme

git-svn-id: https://plugins.svn.wordpress.org/disqus-notify-content-author/trunk@968808 b8457f37-d9ea-0310-8a92-e5e31aec5664
Go back to capitalized form on word Git

git-svn-id: https://plugins.svn.wordpress.org/disqus-notify-content-author/trunk@968813 b8457f37-d9ea-0310-8a92-e5e31aec5664