change the path of image code

* Create select_op design document

* Fix pre-commit issues

* Update select op as per varun's comments

repair hyperlink format

fix space and toctree format

Done

fix https://github.com/PaddlePaddle/Paddle/issues/8921

fix #8956

1. add 1 sentence that was not translated in the original version
2. repair image showing problem

repair link of "Executor"

* update en doc for Distributed Training

* typo fix