Add Justfile listing common commands

[Dietr1ch]

Description

This just lists the commands in the Contributing manual

Checklist

• Change is backwards compatible.

  • Trivially

• Code formatted with nix fmt or
  nix-shell -p treefmt nixfmt deadnix keep-sorted --run treefmt.

  • Doesn't apply, but it passed on my pre-commit hook

• Code tested through nix run .#tests -- test-all or
  nix-shell --pure tests -A run.all.

  • I don't think this is necessary

• Test cases updated/added. See example.

  • Not necessary

• Commit messages are formatted like

  {component}: {description}
  
  {long description}
  

  See CONTRIBUTING for more information and recent commit messages for examples.

• If this PR adds a new module

  • N/A

• If this PR adds an exciting new feature or contains a breaking change.

  • N/A