Yeah that does seem redundant. However, I think the more detailed information dump that the existing text intends to refer to is actually the torguts repository. (which arguably should be under doc/ in the tor repository rather than its own repository)
The torguts repo is a great read. I think it really should move inside tor's doc directory. It would probably be a little better maintained that way too.
Tor doesn't yet use git modules for external repositories, so I guess that would add totally unnecessary complexity.
If simply adding doc/torguts/ with the current torguts files, we'd have to make sure, the current torguts repo is deleted.
Yes, at least until we decide to move the torguts content into the tor repository. doc/HACKING/README.1st.md also mentions torguts.git under a "XXXXX also describe" heading, but I'm not sure that needs to change as part of this ticket.
the torguts repo is directly linked a few lines below though, in the very same file, GettingStarted.md; number 2 of "Getting your first patch into Tor". Wouldn't it be unnecessary to have it on top too?
I think it's fine to mention it both up top and later on in "Getting your first patch into Tor", but only provide the full repository URL in one place.