Add ExtremeElectronics RC2040 (earlephilhower#799)

Fixes earlephilhower#797

Author: earlephilhower

README.md

@@ -25,6 +25,7 @@ See https://arduino-pico.readthedocs.io/en/latest/ along with the examples for m
 * DeRuiLab FlyBoard2040 Core
 * DFRobot Beetle RP2040
 * ElectronicCats Hunter Cat NFC
+* ExtremeElectronics RC2040
 * Invector Labs Challenger RP2040 WiFi
 * Invector Labs Challenger RP2040 WiFi/BLE
 * Invector Labs Challenger NB RP2040 WiFi