Update contributing.md
Update contributing.md

changed < > to html entities.
aerrami/mtools,devkev/mtools,tomzhang/mtools,yaowenqiang/mtools,devkev/mtools,devkev/mtools,gormanb/mtools,parkhyeonghwa/mtools,ces0712/mtools,parkhyeonghwa/mtools,yaowenqiang/mtools,corymintz/mtools,yaowenqiang/mtools,gormanb/mtools,ces0712/mtools,aerrami/mtools,rueckstiess/mtools,tomzhang/mtools,parkhyeonghwa/mtools,ces0712/mtools,aerrami/mtools,tomzhang/mtools,gormanb/mtools,rueckstiess/mtools,corymintz/mtools,corymintz/mtools