readme.txt corrections.

git-svn-id: https://plugins.svn.wordpress.org/simple-hierarchical-sitemap/trunk@787121 b8457f37-d9ea-0310-8a92-e5e31aec5664
Yet another correction in readme file.

git-svn-id: https://plugins.svn.wordpress.org/simple-hierarchical-sitemap/trunk@787122 b8457f37-d9ea-0310-8a92-e5e31aec5664