Add setting screen shoot 

git-svn-id: https://plugins.svn.wordpress.org/x-scroll-to-top-responsive/trunk@949577 b8457f37-d9ea-0310-8a92-e5e31aec5664
Upload screenshot

git-svn-id: https://plugins.svn.wordpress.org/x-scroll-to-top-responsive/trunk@949579 b8457f37-d9ea-0310-8a92-e5e31aec5664