machines: rename to 'hosts/nixos'

This will be more consistent in the future if I want to introduce darwin
or home-manager configurations.

hosts/nixos/porthos/default.nix

@@ -0,0 +1,24 @@
+# Porthos specific settings
+{ ... }:
+
+{
+  imports = [
+    ./boot.nix
+    ./hardware.nix
+    ./home.nix
+    ./networking.nix
+    ./services.nix
+    ./users.nix
+  ];
+
+  # Set your time zone.
+  time.timeZone = "Europe/Paris";
+
+  # This value determines the NixOS release from which the default
+  # settings for stateful data, like file locations and database versions
+  # on your system were taken. It‘s perfectly fine and recommended to leave
+  # this value at the release version of the first install of this system.
+  # Before changing this value read the documentation for this option
+  # (e.g. man configuration.nix or on https://nixos.org/nixos/options.html).
+  system.stateVersion = "20.09"; # Did you read the comment?
+}