Hellooooo!
I think I mostly agree with what you've said.
I've been developing since I was ... dunno ... 12? I'm now 45. Yeh, ancient.
I've spent lots of time in/on Mac, Linux... windows, server side, client side - etc. Too much Java, a little c#, more than 0 C++ (unfortunately), python blah blah blah.
I think where I didn't find it because of unfamiliarity with C# environments. Fine with the code, but I don't spend much/any time with the IDEs (only cos my work has been Mac / Linux for quite some time now). So I didn't automatically make the jump to 'mono' being an option. My last 8 years dev has been primarily on Mac/Linux. So Xcode (cough, splutter), AppCode. Objective-C.
When I downloaded the asset into Unity, I didn't *expect* to have to look inside it for the .zip, because I was, for whatever reason, *expecting* some other external .zip or git repo to get the other stuff from. I had expected that the importable asset was purely game related (which you can argue it still is!). So, what am I saying? hmm... I guess just my direction for where I looked for stuff (code, for example) was based more on how I've seen other stuff done (git, downloadable files / packages) and not necessarily on how it might be done / distributed in Unity...
I'm rambling. I don't think the docs would need much. I'd be happy to write up something if it'd help.
I think something directly off the "TNet3 Tutorials" or a sticky on it's own if you want to keep it separate... both would be fine. btw: the TNET3 Tutorials page was the canonical start point for me. I dug around a bit on the web (this is before I found the .zip and before I looked inside the TNET3 Asset package btw), and the forums / that tutorials page pretty much was where I ended up.
(btw: I got a dedicated server, and my first game clients connecting in about 30m after I worked out where things were at. I'm very happy with what I've seen of TNet so far)
So, without further ado:
(this could be a subpage directly above Examples Overview, in the Overview section of Tutorials).
Dedicated Server
===========
The TNet3 package/assets contain everything you're after. Test scenes, objects, and also the server (see TNetServer.zip inside the asset that you downloaded from Unity).
For linux/mac users: Use 'mono' to run the TNetServer.exe (search this forum, there's quite a few posts about it).
For Mac, Mono can be got a few ways, 'brew' being a good one.
e.g: mono TNServer.exe -ip 192.168.1.61 -tcp 11889 -name MySuperGameOfAwesome
To start with, check out the examples first. These will see/connect to this dedicated server just fine, and provide a good starting point.
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And really, had I know the above, I prob would not have had to post here. But then, I would also not have introduced myself to you wondrous people

So maybe less docs? (no! I'm joking!)