"non-layer add doc for executor module" (#11602)
"non-layer add doc for executor module" (#11602)

* "add doc for exec"

* "add more changes"

* "fix based on preview"

* "chagne code format"

luotao1/Paddle,PaddlePaddle/Paddle,tensor-tang/Paddle,luotao1/Paddle,jacquesqiao/Paddle,PaddlePaddle/Paddle,chengduoZH/Paddle,QiJune/Paddle,QiJune/Paddle,tensor-tang/Paddle,baidu/Paddle,baidu/Paddle,luotao1/Paddle,luotao1/Paddle,reyoung/Paddle,jacquesqiao/Paddle,PaddlePaddle/Paddle,reyoung/Paddle,PaddlePaddle/Paddle,reyoung/Paddle,baidu/Paddle,baidu/Paddle,PaddlePaddle/Paddle,luotao1/Paddle,tensor-tang/Paddle,QiJune/Paddle,reyoung/Paddle,jacquesqiao/Paddle,reyoung/Paddle,baidu/Paddle,chengduoZH/Paddle,jacquesqiao/Paddle,chengduoZH/Paddle,chengduoZH/Paddle,luotao1/Paddle,reyoung/Paddle,tensor-tang/Paddle,jacquesqiao/Paddle,chengduoZH/Paddle,QiJune/Paddle,QiJune/Paddle,luotao1/Paddle,tensor-tang/Paddle,jacquesqiao/Paddle,QiJune/Paddle,PaddlePaddle/Paddle,PaddlePaddle/Paddle