Improved README.
Improved README.

shanetmoore/improved-rack-throttle-w-expiry,teampayoff/rack-throttle,npolar/rack-throttle,dryruby/rack-throttle,spire-inc/rack-throttle,melriffe/rack-throttle,scottwater/rack-throttle,rapind/rack-throttle,bendiken/rack-throttle,WindStill/rack-throttle,kidlab/rack-throttle