Steiner Configuration

Ported over the configuration for steiner into the flake. Have
tested the deployment in a VM and am writing this commit from
the flake itself. Everything came up and this should be good to
pass issue #4 and move this to a Done status.

hosts/steiner.nix

@@ -0,0 +1,5 @@
+{ config, pkgs, ... }:
+
+{
+  networking.hostName = "steiner"; # Define your hostname.
+}