update readme.txt

git-svn-id: https://plugins.svn.wordpress.org/photos-box/trunk@1033568 b8457f37-d9ea-0310-8a92-e5e31aec5664
update readme.txt 2

git-svn-id: https://plugins.svn.wordpress.org/photos-box/trunk@1033569 b8457f37-d9ea-0310-8a92-e5e31aec5664
update readme.txt 3

git-svn-id: https://plugins.svn.wordpress.org/photos-box/trunk@1033570 b8457f37-d9ea-0310-8a92-e5e31aec5664