Add section about % completed
Add section about % completed

It took me a little while to find this stuff and it looks like others have had trouble with it too:
https://github.com/quirkey/resque-status/issues/35
nathan-v/resque-state,compwron/resque-status,georgemillo/resque-status,quirkey/resque-status,quirkey/resque-status,georgemillo/resque-status,compwron/resque-status,nathan-v/resque-state