add brief explanation of DDim usage
add brief explanation of DDim usage

luotao1/Paddle,luotao1/Paddle,chengduoZH/Paddle,pengli09/Paddle,tensor-tang/Paddle,putcn/Paddle,pkuyym/Paddle,reyoung/Paddle,PaddlePaddle/Paddle,lispc/Paddle,putcn/Paddle,Canpio/Paddle,lcy-seso/Paddle,jacquesqiao/Paddle,pengli09/Paddle,pengli09/Paddle,lcy-seso/Paddle,putcn/Paddle,lispc/Paddle,hedaoyuan/Paddle,yu239/Paddle,QiJune/Paddle,lispc/Paddle,tensor-tang/Paddle,reyoung/Paddle,tensor-tang/Paddle,pkuyym/Paddle,pkuyym/Paddle,Canpio/Paddle,hedaoyuan/Paddle,lcy-seso/Paddle,yu239/Paddle,lispc/Paddle,QiJune/Paddle,luotao1/Paddle,QiJune/Paddle,yu239/Paddle,luotao1/Paddle,hedaoyuan/Paddle,chengduoZH/Paddle,pengli09/Paddle,pkuyym/Paddle,baidu/Paddle,PaddlePaddle/Paddle,jacquesqiao/Paddle,PaddlePaddle/Paddle,pkuyym/Paddle,baidu/Paddle,Canpio/Paddle,yu239/Paddle,lispc/Paddle,pkuyym/Paddle,jacquesqiao/Paddle,jacquesqiao/Paddle,QiJune/Paddle,tensor-tang/Paddle,reyoung/Paddle,lispc/Paddle,tensor-tang/Paddle,hedaoyuan/Paddle,reyoung/Paddle,baidu/Paddle,chengduoZH/Paddle,lispc/Paddle,PaddlePaddle/Paddle,putcn/Paddle,jacquesqiao/Paddle,jacquesqiao/Paddle,pengli09/Paddle,Canpio/Paddle,PaddlePaddle/Paddle,Canpio/Paddle,lcy-seso/Paddle,hedaoyuan/Paddle,putcn/Paddle,reyoung/Paddle,hedaoyuan/Paddle,chengduoZH/Paddle,Canpio/Paddle,lcy-seso/Paddle,pengli09/Paddle,lcy-seso/Paddle,luotao1/Paddle,PaddlePaddle/Paddle,lispc/Paddle,putcn/Paddle,QiJune/Paddle,chengduoZH/Paddle,yu239/Paddle,hedaoyuan/Paddle,reyoung/Paddle,luotao1/Paddle,pengli09/Paddle,Canpio/Paddle,yu239/Paddle,pengli09/Paddle,luotao1/Paddle,hedaoyuan/Paddle,yu239/Paddle,baidu/Paddle,PaddlePaddle/Paddle,yu239/Paddle,baidu/Paddle,QiJune/Paddle,Canpio/Paddle