* update links to main branch * update mmdet and mmseg * update readthedocs links
* update the version switcher menu * update rst * update * update
* fix links of docs * [Docs]: Use shared menu from theme instead * [Refactor]: Refactor the directory structure of docs * [Fix]: Fix lint * [Fix]: Fix __version__.py file link bug Co-authored-by: fangyixiao18 <fangyx18@hotmail.com>