Create a specific README.md for Zigbee3.0_Dongle

[Hedda]

@xsp1989 Suggest adding this specific README.md for Zigbee3.0_Dongle as something to start with and some information that could help community firmware developers too. Hopefully, you and others can fix any incorrect information.

Note that I am not a firmware developer and that much of this information was blindly copied from these sources without full insight into their meaning:

https://github.com/grobasoz/zigbee-firmware/blob/master/EFR32%20Series%201/README.md

https://github.com/zha-ng/EZSP-Firmware/blob/master/Elelabs-ELU013/README.md

https://github.com/zha-ng/EZSP-Firmware/blob/master/README.md

https://github.com/grobasoz/zigbee-firmware/blob/master/README.md

https://github.com/zha-ng/EZSP-Firmware/blob/master/EByte-E180-Z120B/README.md

https://github.com/grobasoz/zigbee-firmware/blob/master/Sonoff-ZBBridge/README.md

https://github.com/grobasoz/zigbee-firmware/blob/master/EFR32%20Series%201/README.md

https://github.com/Koenkk/Z-Stack-firmware/blob/master/coordinator/Z-Stack_3.x.0/bin/README.md

[xsp1989]

Thank you very much.