Add support for non-nixos systems

I run Debian on my Thinkpad and wanted to take advantage of nix on there
without also installing NixOS there, so here is added support for it.

non-nixos-install.sh

@@ -0,0 +1,22 @@
+#!/usr/bin/env sh
+
+# This script sets up nix and home-manager for distributions that are not NixOS.
+
+set -e
+BASE_PATH="$(dirname "$(realpath "$0")")"
+
+if [ ! -d "/nix" ]; then
+    # Do multi-user installation
+    sh <(curl -L https://nixos.org/nix/install) --daemon
+    nix-channel --add https://nixos.org/channels/nixpkgs-unstable nixpkgs
+fi
+
+if [ ! -x "$HOME/.nix-profile/bin/home-manager" ]; then
+    ln -svf "$BASE_PATH/users/blank/home-manager" "$HOME/.config/home-manager"
+    ln -svf "$BASE_PATH/users/blank/nixpkgs" "$HOME/.config/nixpkgs"
+
+    nix-channel --add https://github.com/nix-community/home-manager/archive/master.tar.gz home-manager
+    nix-channel --update
+    nix-shell '<home-manager>' -A install
+fi
+