update docs.
update docs.

pfnet/chainer,wkentaro/chainer,okuta/chainer,niboshi/chainer,wkentaro/chainer,niboshi/chainer,wkentaro/chainer,chainer/chainer,hvy/chainer,hvy/chainer,chainer/chainer,okuta/chainer,okuta/chainer,hvy/chainer,niboshi/chainer,hvy/chainer,niboshi/chainer,wkentaro/chainer,okuta/chainer,chainer/chainer,chainer/chainer