Update doc of layers.py
Update doc of layers.py

Canpio/Paddle,luotao1/Paddle,reyoung/Paddle,baidu/Paddle,baidu/Paddle,chengduoZH/Paddle,putcn/Paddle,pkuyym/Paddle,Canpio/Paddle,QiJune/Paddle,luotao1/Paddle,reyoung/Paddle,luotao1/Paddle,QiJune/Paddle,PaddlePaddle/Paddle,chengduoZH/Paddle,pkuyym/Paddle,tensor-tang/Paddle,jacquesqiao/Paddle,Canpio/Paddle,jacquesqiao/Paddle,lcy-seso/Paddle,QiJune/Paddle,tensor-tang/Paddle,luotao1/Paddle,chengduoZH/Paddle,baidu/Paddle,Canpio/Paddle,PaddlePaddle/Paddle,chengduoZH/Paddle,Canpio/Paddle,QiJune/Paddle,lcy-seso/Paddle,pkuyym/Paddle,Canpio/Paddle,Canpio/Paddle,chengduoZH/Paddle,jacquesqiao/Paddle,reyoung/Paddle,putcn/Paddle,PaddlePaddle/Paddle,lcy-seso/Paddle,PaddlePaddle/Paddle,reyoung/Paddle,lcy-seso/Paddle,putcn/Paddle,PaddlePaddle/Paddle,jacquesqiao/Paddle,luotao1/Paddle,putcn/Paddle,pkuyym/Paddle,pkuyym/Paddle,pkuyym/Paddle,baidu/Paddle,jacquesqiao/Paddle,QiJune/Paddle,PaddlePaddle/Paddle,baidu/Paddle,tensor-tang/Paddle,QiJune/Paddle,luotao1/Paddle,luotao1/Paddle,Canpio/Paddle,lcy-seso/Paddle,jacquesqiao/Paddle,reyoung/Paddle,tensor-tang/Paddle,tensor-tang/Paddle,putcn/Paddle,reyoung/Paddle,lcy-seso/Paddle,putcn/Paddle,PaddlePaddle/Paddle