add upgrade guide
add upgrade guide

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