Clarify documentation on identifiers and connections

[rytilahti]

https://developers.home-assistant.io/docs/device_registry_index/#automatic-registration-through-an-entity

A device will be matched up with an existing device via supplied identifiers or connections, like serial numbers or MAC addresses. If identifiers and connections are provided, the device registry will first try to match by identifiers.

This could use some clarification on how these are used and which ones should be set, my understanding is that:

• Identifiers can be anything from hardware-based identifiers (like serial numbers) to config entry ids
• Connections are network-based identifiers such as mac or zigbee addresses

The example on the linked page uses confusingly self.unique_id as a representative for the hue serial number (based on the comment), and does not list any connections that could be useful to exemplify the usage.

[ViViDboarder]

Thanks. I'm still confused if I should be using connections because it's listed under Manual Registration in that documentation.