[Docs] add config docs (#6)

* add config user doc

* add config user doc

* Fix typo

* fix typo

* reference mmcv

* fix typo

* fix typo

* Restructuring config.md

* Update introduction

Co-authored-by: Kai Chen <chenkaidev@gmail.com>

* Fix

Co-authored-by: Zaida Zhou <58739961+zhouzaida@users.noreply.github.com>

* Update docs/zh_cn/tutorials/config.md

Co-authored-by: Zaida Zhou <58739961+zhouzaida@users.noreply.github.com>

* Fix title level

Co-authored-by: Zaida Zhou <58739961+zhouzaida@users.noreply.github.com>

* refactor the doc

* remove **bold** on titles

* Fix python comment

* Fix python comment

* Update docs/zh_cn/tutorials/config.md

Co-authored-by: Zaida Zhou <58739961+zhouzaida@users.noreply.github.com>

Co-authored-by: Kai Chen <chenkaidev@gmail.com>
Co-authored-by: Zaida Zhou <58739961+zhouzaida@users.noreply.github.com>