Improve support for NixOS

[DamienCassou]

In NixOS, there is a /etc/os-release file which contains something like:

NAME=NixOS
ID=nixos
VERSION="20.09.git.54408d8707e (Nightingale)"
VERSION_CODENAME=nightingale
VERSION_ID="20.09.git.54408d8707e"
PRETTY_NAME="NixOS 20.09 (Nightingale)"
LOGO="nix-snowflake"
HOME_URL="https://nixos.org/"
DOCUMENTATION_URL="https://nixos.org/nixos/manual/index.html"
SUPPORT_URL="https://nixos.org/nixos/support.html"
BUG_REPORT_URL="https://github.com/NixOS/nixpkgs/issues"

[retrohacker]

Thanks @DamienCassou ❤️

We support custom parsing of the os-release files by dropping a module in ./logic file named after the distribution as it appears in our os.json file. These are loaded in https://github.com/retrohacker/getos/blob/master/index.js by the customLogic function.