update readme

git-svn-id: https://plugins.svn.wordpress.org/participants-database/trunk@817184 b8457f37-d9ea-0310-8a92-e5e31aec5664
update readme, version numbers

git-svn-id: https://plugins.svn.wordpress.org/participants-database/trunk@817186 b8457f37-d9ea-0310-8a92-e5e31aec5664