update CONTRIBUTING.md
update CONTRIBUTING.md

typos and formatting
eadlam/roslibjs,DLu/roslibjs,harmishhk/roslibjs,chrisl8/roslibjs,BennyRe/roslibjs,jeansebbaklouti/roslibjs,DLu/roslibjs,jeansebbaklouti/roslibjs,harmishhk/roslibjs,BennyRe/roslibjs,kbendick/roslibjs,chrisl8/roslibjs,kbendick/roslibjs,eadlam/roslibjs,DLu/roslibjs,harmishhk/roslibjs,kbendick/roslibjs