Add more documentation for Arduino Giga R1 WiFi

[anthonyhoegberg]

I feel like a there is a lot lacking documentation about the Giga R1 WiFi and how to use it with this library. Also the fact the library is called Portenta OTA makes this even more confusing.

Maybe a new library for the Giga R1 WiFi is needed or a rename of the existing library including more documentation to cover Giga R1 aswell and explain the differences (if any) and how to use it on Giga R1 aswell.

Other stuff like MCUBoot and STM32H747_System might also need more documentation for the Giga R1.

Overall lack of documentation and i would apreaciate if we could do something about it?