set up a default config

modules/nixos/default.nix

@@ -0,0 +1,6 @@
+# Add your reusable NixOS modules to this directory, on their own file (https://nixos.wiki/wiki/Module).
+# These should be stuff you would like to share with others, not your personal configurations.
+{
+  # List your module files here
+  # my-module = import ./my-module.nix;
+}