added French translation files and updated readme

git-svn-id: https://plugins.svn.wordpress.org/related-posts-by-taxonomy/trunk@1015809 b8457f37-d9ea-0310-8a92-e5e31aec5664
updated readme

git-svn-id: https://plugins.svn.wordpress.org/related-posts-by-taxonomy/trunk@1015816 b8457f37-d9ea-0310-8a92-e5e31aec5664