Add ACD3100 library (#5319)

* Update repositories.txt

Arduino library for DAC8560 SPI Digital Analog Convertor (16 bit).

* Update repositories.txt

Arduino library for for I2C ACD3100 CO2 sensor

Author: RobTillaart

repositories.txt

@@ -5204,6 +5204,7 @@ https://github.com/RobTillaart/74HC138
 https://github.com/RobTillaart/74HC154
 https://github.com/RobTillaart/A1301
 https://github.com/RobTillaart/ACD10
+https://github.com/RobTillaart/ACD3100
 https://github.com/RobTillaart/ACS712
 https://github.com/RobTillaart/AD5144A
 https://github.com/RobTillaart/AD520X