add help text- how to stop drawing polygon on /node/add/map-feature

Pretty minor, but suggest adding help text to /node/add/map-feature that says, somehow:
" ...double click to complete your polygon"

...as I couldn't figure out how to stop drawing the polygon, and ended up with a ginormous, jagged, crazy monster of a shape (and then couldn't click other stuff that I needed to, it just kept drawing, ha). Like watching an out of control zombie outbreak that I couldn't turn off... :)