Update CONTRIBUTING.md
Update CONTRIBUTING.md

Minor edits.
Gjacquenot/simbody,elkingtonmcb/simbody,robojukie/simbody,Gjacquenot/simbody,elkingtonmcb/simbody,chrisdembia/simbody,simbody/simbody,elkingtonmcb/simbody,scamille/simbody,chrisdembia/simbody,Gjacquenot/simbody,robojukie/simbody,robojukie/simbody,scamille/simbody,scamille/simbody,simbody/simbody,chrisdembia/simbody