Automatic garbage collection

nixos/base.nix

@@ -202,8 +202,8 @@
   '';
   security.pam.services.sddm.enableGnomeKeyring = true;
 
-  # Allow non free packages
   nixpkgs.config.allowUnfree = true;
+  nix.gc.automatic = true;
 
   # This value determines the NixOS release from which the default
   # settings for stateful data, like file locations and database versions

nixos/thor.nix

@@ -148,6 +148,7 @@
   };
 
   nixpkgs.config.allowUnfree = true;
+  nix.gc.automatic = true;
 
   system.stateVersion = "21.05"; # Did you read the comment?
 }