update readme file

git-svn-id: https://plugins.svn.wordpress.org/oh-add-script-header-footer/trunk@969627 b8457f37-d9ea-0310-8a92-e5e31aec5664
update readme file

git-svn-id: https://plugins.svn.wordpress.org/oh-add-script-header-footer/trunk@969630 b8457f37-d9ea-0310-8a92-e5e31aec5664