update readme.txt

git-svn-id: https://plugins.svn.wordpress.org/manage-issue-based-magazine/trunk@885064 b8457f37-d9ea-0310-8a92-e5e31aec5664
update readme.txt

git-svn-id: https://plugins.svn.wordpress.org/manage-issue-based-magazine/trunk@885065 b8457f37-d9ea-0310-8a92-e5e31aec5664