* [Docs] add faq document

* Update docs/en/faq.md

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

* Update docs/zh_cn/faq.md

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

* modify readme

* modify index.rst

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