link updates in readme.txt

git-svn-id: https://plugins.svn.wordpress.org/custom-post-donations/trunk@936179 b8457f37-d9ea-0310-8a92-e5e31aec5664
corrected readme.txt error

git-svn-id: https://plugins.svn.wordpress.org/custom-post-donations/trunk@936181 b8457f37-d9ea-0310-8a92-e5e31aec5664