TRIVIAL: docs update for service dragging.
TRIVIAL: docs update for service dragging.

R=frankban
CC=
https://codereview.appspot.com/8616047

bac/juju-gui,bac/juju-gui,CanonicalJS/juju-gui,bac/juju-gui,mitechie/juju-gui,mitechie/juju-gui,jrwren/juju-gui,jrwren/juju-gui,bac/juju-gui,CanonicalJS/juju-gui,jrwren/juju-gui,jrwren/juju-gui,mitechie/juju-gui,mitechie/juju-gui,CanonicalJS/juju-gui