Add initial testfiles for home manager

nix/local_machine.nix

@@ -0,0 +1,11 @@
+{ ... }: {
+    # local-machine.nix
+    # This is a template file that is committed to git with minimal changes.
+    # In order to use this and remain pure, each machine needs to create a local branch, i.e `machine-wsl` and set these variables
+    # accordingly, and then commit it.
+    home = {
+        # Stub values for demonstration. Override these in local branch.
+        username = "nixos";
+        homeDirectory = "/home/nixos";
+    };
+}