CONTRIBUTING.md: improve commit guidelines

Internal discussions revealed some minor improvements that could be made
to commit formatting. I did some minor reformatting and other
additions while I was there.
Card origin_cartridge_111 - Updated cartridge versions for stage cut
Merge pull request #4746 from sosiouxme/contributors

Merged by openshift-bot
Test case cleanup
Merge pull request #4744 from mfojtik/latest_versions

Merged by openshift-bot