update readme file

git-svn-id: https://plugins.svn.wordpress.org/last-post-redirect/trunk@841523 b8457f37-d9ea-0310-8a92-e5e31aec5664
tagging version 1.2.1

git-svn-id: https://plugins.svn.wordpress.org/last-post-redirect/trunk@841524 b8457f37-d9ea-0310-8a92-e5e31aec5664