nixos/znc: Doc fix about `services.znc.config`

We need to disable `services.znc.mutable` to make changes apply even
after the first deploy, not enable it (it's already enabled by default).

Changed files
+1 -1
nixos
modules
services
networking
+1 -1
nixos/modules/services/networking/znc/default.nix
···
gracefully be applied to this option.
If you intend to update the configuration through this option, be sure
-
to enable {option}`services.znc.mutable`, otherwise none of the
+
to disable {option}`services.znc.mutable`, otherwise none of the
changes here will be applied after the initial deploy.
'';
};