Document and provide examples of usage for the content scanner

**Is your feature request related to a problem? Please describe.**

I'm having trouble understanding how the content scanner is supposed to be used (I'm fairly new to this, so apologies if I'm missing something obvious here). How is the API supposed to be consumed - are clients referring to it, do you put a reverse proxy in front of (your) homeserver that intercepts requests to media and passes them to the scanner, other approaches? I'm not sure what is possible and also what is recommended.

**Describe the solution you'd like**

Ideally there is documentation on how you can use this with a home server and an example conf in case something additional is required (on homeserver.yaml or a reverse proxy setup)

**Describe alternatives you've considered**

I considered trying this with a reverse proxy, though I still wanted to open this request for docs - if there are clarifying comments on the request, I can open a doc PR.

**Additional context**

Hope to have a tutorial and examples under docs/ folder.