Readme update
Readme update

Reflects the new option to convert preexisting mp4 files to match
current codec settings.

phtagn/sickbeard_mp4_automator,phtagn/sickbeard_mp4_automator,Collisionc/sickbeard_mp4_automator,Collisionc/sickbeard_mp4_automator,Filechaser/sickbeard_mp4_automator,Filechaser/sickbeard_mp4_automator