docs: update customizing section to reflect service dependencies

[maschad]

Closes #1763

[vmx]

I was using my on configuration and was just using the pubsub service. That isn't enough, it won't find the other peers. You would also need the identify service to make it work. That should be added to the docs (thanks @achingbrain for pointing that out).

[maschad]

Thanks for pointing that out @vmx I've updated it.

[vmx]

Thanks for pointing that out @vmx I've updated it.

In the other sections the identify service is explicitly mentioned in the description and not only the code. Would it make sense to do the same for pubusb?

[maschad]

In the other sections the identify service is explicitly mentioned in the description and not only the code. Would it make sense to do the same for pubusb?

That's a good point. When I listed the Potential methods for discovering peers I thought that may suggest that identify protocol is implicit, but I think it would be clearer to add it explicitly.