[Docs request] FENIX module backpack

[Unb0rn]

The documentation mentions that backpack supports the Fenix module. However no additional data on required hardware/wiring(?)/setup is present. It is very confusing - if I understood it correctly, it should be compatible with this module by JyeSmith. This module itself has a ESP32 module onboard and even more, it has ExpressLRS options in its' OSD - I think there was some prototype to use this module as a controller for all backpacks. It would be very nice to have some docs on required hardware, on wiring (should it be connected via SPI as any other rx5808 module?) and so on.