@HarmlessSaucer This is something different. There’s HomeKit and then there’s HomeKit Controller. You’re talking about the HomeKit component which is an alternative to Homebridge (which you don’t need to add to discovery to have work, it has nothing to do with discovery), and the other posters are talking about HomeKit Controller.
To the users above, check this post and see if it fixes your problem: Support for control of HomeKit bulbs and switches (testing required!). Unfortunately if you’re using Docker or Hass.io changes will need to be made to the Docker image to add the required dependencies.