Improve docs of depth2space
Improve docs of depth2space

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