Document how to silence the ready message
Document how to silence the ready message

Describe how to suppress the "Ready to catch errors" message in the README.

looker/raven-ruby,getsentry/raven-ruby,nateberkopec/raven-ruby,sunkencity/raven-ruby,spredfast/raven-ruby,timcheadle/raven-ruby,ShakrMedia/raven-ruby,if1live/raven-ruby,zanker/raven-ruby,jakecraige/raven-ruby,lsb/raven-ruby,alyssa/raven-ruby