added quadlet-nix input, created initial ixion config, created wrapper around quadlets

also wrote some doucumentation about quadlets, nothing too comprehesive
though as the wrapper might get removed later

modules/machine/ixion/default.nix

@@ -0,0 +1,6 @@
+{...}: {
+  imports = [
+    ./configuration.nix
+    ./hardware-configuration.nix
+  ];
+}