update readme and add banner

git-svn-id: https://plugins.svn.wordpress.org/quotable/trunk@894436 b8457f37-d9ea-0310-8a92-e5e31aec5664
shorten description in readme

git-svn-id: https://plugins.svn.wordpress.org/quotable/trunk@894439 b8457f37-d9ea-0310-8a92-e5e31aec5664
update readme

git-svn-id: https://plugins.svn.wordpress.org/quotable/trunk@894443 b8457f37-d9ea-0310-8a92-e5e31aec5664