NixOS modules move one level up because it's unlikely that //ops/nixos
will contain actual systems at this point (they're user-specific).
This is the first users folder, so it is also added to the root
readTree invocation for the repository.
Change-Id: I546c701145fa204b7ba7518a8a56a783588629e0
Reviewed-on: https://cl.tvl.fyi/c/depot/+/244
Reviewed-by: tazjin <mail@tazj.in>
