Refine the doc of layers.py
Refine the doc of layers.py

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