nixos/sudo-conf: fix doas rule to include path

nix/nixosModules/common/sudo-conf.nix

@@ -8,10 +8,18 @@
     enable = true;
     extraRules = [
       {
-        # invoke just with doas directly as a nixos-rebuild helper
+        # Invoke just with doas directly as a nixos-rebuild helper
+        #
+        # Specifiying just here is impractical, because
+        # - Use absolute path?
+        #   Works only for a specific version of just binary.
+        #   Also, for some reason, the rule won't match.
+        # - Use relative path?
+        #   doas's docs says it searches in a "limited subset of PATH" if it's relative.
+        #   I suspect that it doesn't search the PATH added ad-hoc by the nix-shell, also not a good solution.
+        #   Also, for some reason, the rule won't match.
         users = [":wheel"];
         setEnv = ["PATH"];
-        cmd = "just";
       }
     ];
   };