Document how to setup for home-manager's NixOS module

[ametis70]

Is your feature request related to a problem? Please describe.
I read the documentation and I understood how to setup completion for NixOS and home-manager options when Home-Manager is installed in it's standalone mode, but I cannot make the options show up when using the NixOS Module

Describe the solution you'd like
I'd like to make the options to show up. Is it even possible? If so, I believe it should be documented alongside the other examples.

Describe alternatives you've considered
N/A

Additional context
N/A

Thanks in advance!

[inclyc]

I'd like to make the options to show up. Is it even possible?

Yes, it is possible. You can refer to #615 (comment) for a simple solution, (i.e. use getSuboptions).

If so, I believe it should be documented alongside the other examples.

Yes, we can add it to the documentation, or if you figured it out, feel free to make PRs.

[ametis70]

Great, that worked perfectly. I'll make a PR to add it to the documentation. Thanks!