Add CONTRIBUTING.md
Add CONTRIBUTING.md

takeshineshiro/ReactiveViewModel,SummerHanada/ReactiveViewModel,ashfurrow/ReactiveViewModel,nickcheng/ReactiveViewModel,jackgao2016/ReactiveViewModel,fxd/ReactiveViewModel,iguchunhui/ReactiveViewModel,jackgao2016/ReactiveViewModel,fxd/ReactiveViewModel,TeehanLax/ReactiveViewModel,ReactiveCocoa/ReactiveViewModel,ReactiveCocoa/ReactiveViewModel,iguchunhui/ReactiveViewModel,nickcheng/ReactiveViewModel,nickcheng/ReactiveViewModel,SummerHanada/ReactiveViewModel,takeshineshiro/ReactiveViewModel,ashfurrow/ReactiveViewModel