FastAPI integration docs

[leplatrem]

Merge into #75

[leplatrem]

Some of the documentation we've added feels like documentation of FastAPI vs how to integrate Dockerflow's FastAPI extension into a FastAPI app.

This is true about all the rest of the documentation I believe, I aligned it with other integrations actually.

Can we link to FastAPI documentation where appropriate and focus this documentation on aspects that are Dockerflow-specific?

Will see what I can do...

[grahamalama]

This is true about all the rest of the documentation I believe, I aligned it with other integrations actually.

Ahh okay. Well then, I think internal consistency outweighs that feedback I gave. Maybe look for places were we're missing integration docs, but if that spills into FastAPI documentation, so be it.