Centralize Nix development workflow guides

[phated]

Problem

Right now, we just copy-paste the nix development workflow across the repositories that use Nix. Eventually this will be all repos and will be hard to maintain.

Proposed solution

We should document this in one place and link to it from each repo that relies on the nix dev flow.

Alternatives considered

No response

Additional context

No response

Submission Checklist

• Once I hit submit, I will assign this issue to the Project Board with the appropriate tags.