Update read me to correctly display screenshot. Argh.

git-svn-id: https://plugins.svn.wordpress.org/thumbnail-grid/trunk@849017 b8457f37-d9ea-0310-8a92-e5e31aec5664
Fix Readme so that screenshot text sends users to web site for demos.

git-svn-id: https://plugins.svn.wordpress.org/thumbnail-grid/trunk@849022 b8457f37-d9ea-0310-8a92-e5e31aec5664