Vagga on NixOS

[tailhook]

It should at least be documented. But probably NixOS should have a module for vagga.

First thing that module needs is subuid ranges:

    subUidRanges = [
      { startUid = 100000; count = 65536; }
    ];
    subGidRanges = [
      { startGid = 100000; count = 65536; }
    ];