Add comments for key

Co-authored-by: Robert Hensing <roberth@users.noreply.github.com>

modules/nixosModules.nix

@@ -17,6 +17,11 @@ in
         default = { };
         apply = mapAttrs (k: v: {
           _file = "${toString moduleLocation}#nixosModules.${k}";
+          # Note: this neglects to represent potential differences due to input
+          #       overrides or flake-parts extendModules. However, the cost for this
+          #       is too high or plain infeasible respectively. We choose to implement
+          #       deduplication and disabledModules regardless, because not doing
+          #       so poses a more direct problem.
           key = "${toString moduleLocation}#nixosModules.${k}";
           imports = [ v ];
         });