Add MHZC02 (#2341)

Arduino Library for MHZ series CO2 sensors.

Author: RobTillaart

repositories.txt

@@ -3580,6 +3580,7 @@ https://github.com/RobTillaart/MCP23S08
 https://github.com/RobTillaart/MCP23S17
 https://github.com/RobTillaart/MCP4725
 https://github.com/RobTillaart/MCP9808_RT
+https://github.com/RobTillaart/MHZCO2
 https://github.com/RobTillaart/MINMAX
 https://github.com/RobTillaart/ML8511
 https://github.com/RobTillaart/moduloMap