Updated readme to reflect tested up to WP 3.8.1

git-svn-id: https://plugins.svn.wordpress.org/wp-post-to-pdf-enhanced/trunk@845461 b8457f37-d9ea-0310-8a92-e5e31aec5664
Working on custom footer capability

git-svn-id: https://plugins.svn.wordpress.org/wp-post-to-pdf-enhanced/trunk@845463 b8457f37-d9ea-0310-8a92-e5e31aec5664