[Doc] "Model Serving" Chinese doc in useful_tools.md (#761)

* Add Model Serving Chinese docs

* Update docs_zh-CN/useful_tools.md

Co-authored-by: Junjun2016 <hejunjun@sjtu.edu.cn>

* Update useful_tools.md

* fix lint error

Co-authored-by: Junjun2016 <hejunjun@sjtu.edu.cn>