Fix contribution guide for CuPy separation
Fix contribution guide for CuPy separation

aonotas/chainer,keisuke-umezawa/chainer,okuta/chainer,rezoo/chainer,jnishi/chainer,jnishi/chainer,chainer/chainer,chainer/chainer,delta2323/chainer,wkentaro/chainer,okuta/chainer,tkerola/chainer,jnishi/chainer,ktnyt/chainer,ysekky/chainer,ktnyt/chainer,jnishi/chainer,hvy/chainer,chainer/chainer,pfnet/chainer,niboshi/chainer,ktnyt/chainer,wkentaro/chainer,anaruse/chainer,ktnyt/chainer,hvy/chainer,keisuke-umezawa/chainer,okuta/chainer,niboshi/chainer,kiyukuta/chainer,niboshi/chainer,keisuke-umezawa/chainer,hvy/chainer,ronekko/chainer,niboshi/chainer,chainer/chainer,wkentaro/chainer,wkentaro/chainer,hvy/chainer,keisuke-umezawa/chainer,kashif/chainer,okuta/chainer