Updated readme with youtube video

git-svn-id: https://plugins.svn.wordpress.org/wp-pipes/trunk@871158 b8457f37-d9ea-0310-8a92-e5e31aec5664
Updated readme with youtube video & added checking environment box

git-svn-id: https://plugins.svn.wordpress.org/wp-pipes/trunk@871159 b8457f37-d9ea-0310-8a92-e5e31aec5664