* Update demo in get started tutorial

* Update demo tutorial

* Refactor the pytorch demo

* Add outline and titles to the demo tutorial.

* Move file and change title

* Add shuffle in dataloader arguments.

* Improve according to comments

* add introduction of mmengine in get_started.md

* resolve comments

* resolve comments

* resolve comments

* resolve comments

* resolve comments

* resolve comments

* update figs

* Add installation docs

* fix typo