Added screenshots.

git-svn-id: https://plugins.svn.wordpress.org/dashboard-notes/trunk@896851 b8457f37-d9ea-0310-8a92-e5e31aec5664
Updated readme with screenshots.

git-svn-id: https://plugins.svn.wordpress.org/dashboard-notes/trunk@896852 b8457f37-d9ea-0310-8a92-e5e31aec5664