Request: add instructions to serve documentation locally

[DeflateAwning]

It would be awesome if you could add instructions to serve the documentation locally. It should go in either the README, in the CONTRIBUTING.md file, or maybe both.

[python-and-novella]

By running pip install poetry,you will get poetry.Then you could clone repo to empty dir.
After you cloned repo,in repo's root,run poetry install firstly,then run poetry run python main.py.
It is very simply.

[rodja]

The quickest way may be docker run -p 8080:8080 zauberzeug/nicegui. I created #3305 to add this to the docs.

[DeflateAwning]

Awesome, thanks a lot!