Update image to reflect depreciation of PUID and GUID
### Proposed Change

The Unraid installation instructions still contain reference to setting the PUID and GUID in the provided image (Key 3 and 4), which I believe have been depreciated as environment variables. It may also be useful to explicitly indicate somewhere (e.g., the main README's parameter section) that these no longer do anything when specified - I've seen a lot of examples online where they are still included. 

### Wiki Page Link

https://github.com/homebridge/docker-homebridge/wiki/Homebridge-on-Unraid