Update readme for 3.9.2 release.

git-svn-id: https://plugins.svn.wordpress.org/contact-form-7/trunk@975983 b8457f37-d9ea-0310-8a92-e5e31aec5664
Update POT file.

git-svn-id: https://plugins.svn.wordpress.org/contact-form-7/trunk@975987 b8457f37-d9ea-0310-8a92-e5e31aec5664