Update PRERELEASE for branch

MSP-10039
Update Contributing

MSP-10039
Fix newlines

MSP-10039
Complete downstream dependencies

MSP-10039
Moving README's Contributing section to its own file

MSP-10039
Move version bump to Release steps

MSP-10039

This way it is the responsibility of a trusted contributor to change the
version instead of the pull requester.
Remove JRuby release instructions

MSP-10039

metasploit-concern does not have a different release for JRuby.
Package CONTRIBUTING.md

MSP-10039
Fix typo

MSP-10039
Merge pull request #5 from rapid7/feature/MSP-10039/readme

README and CONTRIBUTING