Update readme description of RAT and DRAT.
Update readme description of RAT and DRAT.

lewismc/drat,sfrancus/drat,karanjeets/drat,karanjeets/drat,chrismattmann/drat,sfrancus/drat,karanjeets/drat,lewismc/drat,chrismattmann/drat,karanjeets/drat,karanjeets/drat,sfrancus/drat,chrismattmann/drat,sfrancus/drat,chrismattmann/drat,lewismc/drat,lewismc/drat,lewismc/drat,sfrancus/drat,chrismattmann/drat