[Docs] Refactor model.md (#674)

* Refactor model.md

* minor refine

* Fix as comment

* Fix error link

* Fix as comment

* Fix as comment

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

* replace Dataloader with DataLoader

* minor refine

* resolve conflict

* fix render code block

* Fix error link

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