More info on UUIDs

Perhaps UUIDs could have their own page in docs, and be linked from all other pages? They [cause some confusion](https://github.com/exercism/red/issues/31#issuecomment-1114344639), and info on them is [spread in documentation](https://github.com/exercism/docs/search?q=uuid), main info on them being in [*concept exercises* section of config.json docs](https://github.com/exercism/docs/blob/ac587062b6bcc4c2258a3a81036f6377db4acdaa/building/tracks/config-json.md#concept-exercises).