add upgrade notice

git-svn-id: https://plugins.svn.wordpress.org/wp-quick-navi/trunk@1025806 b8457f37-d9ea-0310-8a92-e5e31aec5664
Version 2.2

git-svn-id: https://plugins.svn.wordpress.org/wp-quick-navi/trunk@1025808 b8457f37-d9ea-0310-8a92-e5e31aec5664