Improve documentation for discovery ports

[fice-t]

On the Networking page:

1. Service Discovery states that DLNA also uses port 1900:

DLNA also uses this port

What else, relevant to Jellyfin, uses port 1900? A quick search for 1900 in the Jellyfin org only yielded the DLNA plugin using this port. The "also" should be removed if nothing else uses the port, otherwise there should be a mention of other users of the port. If it is only for general UPnP, then perhaps UPnP should be mentioned?

2. Client Discovery heading states the UDP protocol explicitly, while Service Discovery, which also uses UDP, does not. Perhaps the Service Discovery and HTTP(S) sections should explicitly state the protocols in their headers as well?

3. DLNA here should link to the DLNA subpage, which in turn could link to some external site which describes what DLNA actually is.

4. I found the wording in the discovery sections a bit confusing. Both Service Discovery and Client Discovery both talk about client discovery. It would be nice if it clearly differentiated the usage of each port.

[felix920506]

If you already know how to fix the errors you mentioned, please open a pull request.