Add Changelog to README.txt

git-svn-id: https://plugins.svn.wordpress.org/hideshowpassword/trunk@815886 b8457f37-d9ea-0310-8a92-e5e31aec5664
Add Changelog to README.txt

git-svn-id: https://plugins.svn.wordpress.org/hideshowpassword/trunk@815887 b8457f37-d9ea-0310-8a92-e5e31aec5664