Update repositories.txt (#6272)

Arduino library for the 74HC590 8 bit binary counter.

Author: RobTillaart

repositories.txt

@@ -5443,6 +5443,7 @@ https://github.com/Robox-Robotics/Grove-Offline-Voice-Recognition-Module
 https://github.com/RobPo/Paperino
 https://github.com/RobTillaart/74HC138
 https://github.com/RobTillaart/74HC154
+https://github.com/RobTillaart/74HC590
 https://github.com/RobTillaart/A1301
 https://github.com/RobTillaart/ACD10
 https://github.com/RobTillaart/ACD3100