Added PHP version warning, updated readme

git-svn-id: https://plugins.svn.wordpress.org/fancy-gallery/trunk@989597 b8457f37-d9ea-0310-8a92-e5e31aec5664
Updated Fancy Gallery Readme

git-svn-id: https://plugins.svn.wordpress.org/fancy-gallery/trunk@989599 b8457f37-d9ea-0310-8a92-e5e31aec5664