update the description in readme.txt

git-svn-id: https://plugins.svn.wordpress.org/qqworld-auto-save-images/trunk@983933 b8457f37-d9ea-0310-8a92-e5e31aec5664
update description in readme.txt again

git-svn-id: https://plugins.svn.wordpress.org/qqworld-auto-save-images/trunk@983934 b8457f37-d9ea-0310-8a92-e5e31aec5664