The README is unclear on how to play the singleplayer campaign

[MightyKnight]

Issue

The README does not really help newcomers find out how to play the main campaign.

It only explains how to play custom maps from the Steam Workshop, but doesn't describe for example how one would play the Black Mesa singleplayer campaign together.

Citing "Campaign Support" section:

🌎 Campaign Support

Black Mesa

Visit our Steam Workshop Collection to check out all available custom maps supported by SourceCoop!
[...]

[ak47toh]

It only explains how to play custom maps from the Steam Workshop, but doesn't describe for example how one would play the Black Mesa singleplayer campaign together.

The Readme only applies to server owners who wants to upload Workshop maps/campaigns into their server. Black Mesa official campaign is already provided by default.

First and foremost, are you asking here as a player or as a server owner? If you aren't here to setup a server and only wants to play with friends, just join any public servers that have "co-op" server titles. Usually once in the server you just have to type /coopmenu in chat to choose what maps you want to play. But that's up to whether those servers will display/informing players what commands there are available or not.