fix(darwin): correct typo during user creation (#36)

The darwin template was failing for me, until I changed user creation to `users.users.${username}`.

Co-authored-by: Dusty Pomerleau <dustypomerleau@users.noreply.github.com>
Reviewed-on: #36
Co-authored-by: Dusty Pomerleau <dustypomerleau@noreply.git.auxolotl.org>
Co-committed-by: Dusty Pomerleau <dustypomerleau@noreply.git.auxolotl.org>

darwin/flake.nix

@@ -76,7 +76,7 @@
                 };
               };
               # Here we can create our user
-              uses.users.${username} = {
+              users.users.${username} = {
                 home = "/Users/${username}";
               };