add README.md

git-svn-id: https://plugins.svn.wordpress.org/flickr-picture-backup/trunk@977718 b8457f37-d9ea-0310-8a92-e5e31aec5664
Don`t change at preview page

git-svn-id: https://plugins.svn.wordpress.org/flickr-picture-backup/trunk@977719 b8457f37-d9ea-0310-8a92-e5e31aec5664