Add some friendly (and realistic) contribution info

[niccofyren]

Let's aim to get frontend and backend repo into a state where it is clear what it does, and how to contribute

A couple of possible actions

• Add tg.no section to READMEs
• Update setup steps to make sure they will work for "anyone" (probably already quite ok?)
• Write basic contribution guideline and link to or include in main READMEs (should probably be the same for both backend and frontend)
  • Be nice
  • Create PR that outlines what, why and how
  • Create, reference and follow issues whenever possible
  • Don't pick an issue where someone is already assigned
  • Your contribution might be rejected for a variety of reasons
• Turn of any github repo tools we don't use (discussions is perhaps the only one?)