add comments in gru_step_layer of layers.py to explain the parameter location
add comments in gru_step_layer of layers.py to explain the parameter location

wen-bo-yang/Paddle,livc/Paddle,yu239/Paddle,cxysteven/Paddle,wen-bo-yang/Paddle,Canpio/Paddle,luotao1/Paddle,emailweixu/Paddle,chengduoZH/Paddle,putcn/Paddle,wen-bo-yang/Paddle,lcy-seso/Paddle,yu239/Paddle,luotao1/Paddle,baidu/Paddle,pkuyym/Paddle,PaddlePaddle/Paddle,QiJune/Paddle,QiJune/Paddle,PaddlePaddle/Paddle,putcn/Paddle,luotao1/Paddle,pkuyym/Paddle,lispc/Paddle,pengli09/Paddle,lcy-seso/Paddle,QiJune/Paddle,Canpio/Paddle,yu239/Paddle,pengli09/Paddle,hedaoyuan/Paddle,pengli09/Paddle,livc/Paddle,luotao1/Paddle,hedaoyuan/Paddle,chengduoZH/Paddle,putcn/Paddle,lispc/Paddle,emailweixu/Paddle,livc/Paddle,hedaoyuan/Paddle,lcy-seso/Paddle,PaddlePaddle/Paddle,gangliao/Paddle,tensor-tang/Paddle,gangliao/Paddle,reyoung/Paddle,reyoung/Paddle,jacquesqiao/Paddle,PaddlePaddle/Paddle,livc/Paddle,baidu/Paddle,livc/Paddle,baidu/Paddle,cxysteven/Paddle,pkuyym/Paddle,putcn/Paddle,emailweixu/Paddle,gangliao/Paddle,pengli09/Paddle,cxysteven/Paddle,livc/Paddle,luotao1/Paddle,chengduoZH/Paddle,cxysteven/Paddle,baidu/Paddle,gangliao/Paddle,putcn/Paddle,Canpio/Paddle,luotao1/Paddle,PaddlePaddle/Paddle,Canpio/Paddle,jacquesqiao/Paddle,lcy-seso/Paddle,lispc/Paddle,baidu/Paddle,jacquesqiao/Paddle,QiJune/Paddle,hedaoyuan/Paddle,cxysteven/Paddle,pkuyym/Paddle,pengli09/Paddle,chengduoZH/Paddle,gangliao/Paddle,cxysteven/Paddle,hedaoyuan/Paddle,Canpio/Paddle,lispc/Paddle,emailweixu/Paddle,PaddlePaddle/Paddle,pengli09/Paddle,livc/Paddle,emailweixu/Paddle,wen-bo-yang/Paddle,jacquesqiao/Paddle,reyoung/Paddle,tensor-tang/Paddle,jacquesqiao/Paddle,tensor-tang/Paddle,Canpio/Paddle,tensor-tang/Paddle,QiJune/Paddle,lispc/Paddle,chengduoZH/Paddle,reyoung/Paddle,reyoung/Paddle,hedaoyuan/Paddle,hedaoyuan/Paddle,lcy-seso/Paddle,jacquesqiao/Paddle,emailweixu/Paddle,pkuyym/Paddle,wen-bo-yang/Paddle,yu239/Paddle,gangliao/Paddle,gangliao/Paddle,hedaoyuan/Paddle,lispc/Paddle,QiJune/Paddle,wen-bo-yang/Paddle,yu239/Paddle,lcy-seso/Paddle,pkuyym/Paddle,PaddlePaddle/Paddle,luotao1/Paddle,yu239/Paddle,emailweixu/Paddle,wen-bo-yang/Paddle,pengli09/Paddle,pengli09/Paddle,lispc/Paddle,lispc/Paddle,reyoung/Paddle,yu239/Paddle,putcn/Paddle,Canpio/Paddle,tensor-tang/Paddle,cxysteven/Paddle,yu239/Paddle,Canpio/Paddle