removed original screenshots and updated readme

git-svn-id: https://plugins.svn.wordpress.org/flickr-field-for-advanced-custom-fields/trunk@961066 b8457f37-d9ea-0310-8a92-e5e31aec5664
readme update

git-svn-id: https://plugins.svn.wordpress.org/flickr-field-for-advanced-custom-fields/trunk@961068 b8457f37-d9ea-0310-8a92-e5e31aec5664