Improve documents of updaters
Improve documents of updaters

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