README: Add Ethernet boards list

Author: pennam

README.md

@@ -14,6 +14,7 @@ The `ArduinoIoTCloud` library is the central element of the firmware enabling ce
 * **GSM**: [`MKR GSM 1400`](https://store.arduino.cc/arduino-mkr-gsm-1400-1415)
 * **5G**: [`MKR NB 1500`](https://store.arduino.cc/arduino-mkr-nb-1500-1413)
 * **LoRa**: [`MKR WAN 1300/1310`](https://store.arduino.cc/mkr-wan-1310)
+* **Ethernet**: [`Portenta H7`](https://store.arduino.cc/products/portenta-h7) + [`Vision Shield Ethernet`](https://store.arduino.cc/products/arduino-portenta-vision-shield-ethernet), [`Max Carrier`](https://store.arduino.cc/products/portenta-max-carrier), [`Breakout`](https://store.arduino.cc/products/arduino-portenta-breakout), [`Portenta Machine Control`](https://store.arduino.cc/products/arduino-portenta-machine-control)
 
 ### How?
 1) Register your Arduino IoT Cloud capable board via [Arduino IoT Cloud](https://create.arduino.cc/iot) (Devices Section).