[Docs] Migrate model from mmcv (#473)

* migrate model

* fix title error

* refine as comment

* fix as comment

* minor refine

* Fix as comment

* Update docs/zh_cn/migration/migrate_model_from_mmcv.md

* Update docs/zh_cn/migration/migrate_model_from_mmcv.md

Co-authored-by: Qian Zhao <112053249+C1rN09@users.noreply.github.com>