better doku, fixed a typo

git-svn-id: https://plugins.svn.wordpress.org/rss-import/trunk@957410 b8457f37-d9ea-0310-8a92-e5e31aec5664
typo

git-svn-id: https://plugins.svn.wordpress.org/rss-import/trunk@957415 b8457f37-d9ea-0310-8a92-e5e31aec5664