sage: If docs are not enabled then don't include a doc attribute
there should be no doc attribute if docs are not enabled
the doc attribute is used in nixos/documentation.nix
https://github.com/NixOS/nixpkgs/blob/adeb7629fc6ccf986ccc7013efc60d5e6d5269f1/nixos/modules/misc/documentation.nix#L342
the doc will still be built because the doc attribute exists