[Feature]: nixos module support and documentation.

[blargg]

What's missing?

This is on the roadmap, but the linked issue is #79, which is closed.

We should have module support for nixos. This should have an option to enable jupyter lab (or jupyter hub) as a systemd service.

We should have documentation with a simple example of how to incorporate this into a nixos config.

Possible solution

Add the module in a flake. Users can install the flake which will expose all the settings (like which kernels are enabled) in settings for nixos.

Alternatives

Incorporate this into nixos directly. This looks like more work, as we would have to merge this flake in. I think it would be better to keep it as a separate flake for now.

Additional context

No response