nixos-version: Add missing options

[pyrotelekinetic]

nixos-version was missing the --configuration-revision and --json options. I'm not a zsh user; I have not tested this. I thought it made sense to update this here while I was already doing the same on nix-bash-completions#27

[SebTM]

Thanks for your submission/bringing this issue up, sadly it was not working as expected so I did my best to fix it - completion looks now like this:

I would appreciate one review/tester before I go ahead and merge ✌🏻

[SebTM]

// cc @theesm (can't add you as reviewer) @Mic92

[Mic92]

// cc @theesm (can't add you as reviewer) @Mic92

What do you want me to do? A review?

[SebTM]

If you like to, but mainly I was marking you also because of the issue with @theesm as he wanted to join as well/had contact with you in #44 (no permissions to check team myself I guess, can't see a matching category in settings)