Add docs for mounting Mesop app

[wwwillchen]

The FastAPI example seems to be working well:
https://github.com/wwwillchen/mesop-fastapi

However, I'm having trouble with the Flask example: https://github.com/wwwillchen/mesop-flask - when I try to run Mesop in debug mode, it's not loading.

All things considered though, I think encouraging people to use FastAPI is better as it reduces the likelihood of a version dependency conflict with Mesop's internal Flask usage and other people's Flask usage.

Fixes #803.

[richard-to]

Nice. This is exciting. It could be good to provide examples of how one could interact with Fast API in your example repo.

Also could be good to know what limitations there are at the moment.

[wwwillchen]

Nice. This is exciting. It could be good to provide examples of how one could interact with Fast API in your example repo.

I updated the readme to be clearer about this - there's an HTTP interaction w/ web component, let me know if you're thinking of something else.

Also could be good to know what limitations there are at the moment.

good idea, added one around hot reloading.

[richard-to]

I updated the readme to be clearer about this - there's an HTTP interaction w/ web component, let me know if you're thinking of something else.

Ah, yeah I totally missed that (didn't end up looking at web_component.js).

I guess I was wondering if there was a way to access state from Fast API. One use case I was thinking about was the download use case, where we have some data in state that needs to be included in the download.

It's not a huge deal if we can't access state from from FastAPI. We'd just have to use the web component as a proxy to send certain state info to Fast API.