Document known limitations

This is a Gold rule. In quality_scale.yaml, it is called docs-known-limitations.

The integration page on home-assistant.io lists what the integration cannot do, or cannot do well, by design or because of the device or service. Limitations are not bugs: bugs belong in the issue tracker on GitHub, not in the documentation.

Users find out about a limitation sooner or later. Finding out from the documentation, before they buy a device or spend an evening on an automation, is a lot better than finding out from a failed attempt and an issue that gets closed as "works as intended".

Being upfront about limits also saves you support questions.

## Known limitations

- The integration cannot reboot the device. Use the app of the
  manufacturer for that.
- The cloud API updates the energy usage once per hour, so the energy
  sensors lag up to an hour behind.

See Write integration documentation and the integration page structure for where this section goes.

Checked in review, usually on the documentation pull request.

If the integration has no known limitations, this rule does not apply.