update the readme file

git-svn-id: https://plugins.svn.wordpress.org/fixed-social-icons/trunk@1001398 b8457f37-d9ea-0310-8a92-e5e31aec5664
update the readme file

git-svn-id: https://plugins.svn.wordpress.org/fixed-social-icons/trunk@1001399 b8457f37-d9ea-0310-8a92-e5e31aec5664