Refine the design doc for ctc_beam_search_decoder
Refine the design doc for ctc_beam_search_decoder

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