Updated instructions in the admin page.

git-svn-id: https://plugins.svn.wordpress.org/embed-google-map/trunk@1039329 b8457f37-d9ea-0310-8a92-e5e31aec5664
Added a missing dot.

git-svn-id: https://plugins.svn.wordpress.org/embed-google-map/trunk@1039331 b8457f37-d9ea-0310-8a92-e5e31aec5664