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

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