Make note for moving development to github

git-svn-id: http://plugins.svn.wordpress.org/wp-mpdf/trunk@683987 b8457f37-d9ea-0310-8a92-e5e31aec5664
MPDF updated

git-svn-id: http://plugins.svn.wordpress.org/wp-mpdf/trunk@683988 b8457f37-d9ea-0310-8a92-e5e31aec5664
Fixed readme
Merge branch 'master' of github.com:fkrauthan/wp-mpdf