updated readme.txt description

git-svn-id: https://plugins.svn.wordpress.org/wp-lightbox-bank/trunk@993219 b8457f37-d9ea-0310-8a92-e5e31aec5664
update readme.txt

git-svn-id: https://plugins.svn.wordpress.org/wp-lightbox-bank/trunk@993223 b8457f37-d9ea-0310-8a92-e5e31aec5664