[Debian-salsa-ci] Salsa CI documentation improvements

[Otto Kekäläinen]

Hi!

I am currently trying to simplify/improve the documentation about
Salsa CI. I am for example removing mentions that Salsa CI is
"work-in-progress" and I am trying to make the onboarding instructions
simpler and have less optionality.

Do you have any wishes regarding the documentation or papercuts that
have annoyed you?

Let me know and I will try to incorporate all ideas in this iteration.


Very *early* draft at
https://salsa.debian.org/salsa-ci-team/pipeline/-/merge_requests/519