Update repositories.txt

Add ERCFS Arduino library for SPI based ERCFS rotary encoder.

Author: RobTillaart

repositories.txt

@@ -5438,6 +5438,7 @@ https://github.com/RobTillaart/DS2438
 https://github.com/RobTillaart/DS28CM00
 https://github.com/RobTillaart/DS3232
 https://github.com/RobTillaart/ellipse
+https://github.com/RobTillaart/ERCFS
 https://github.com/RobTillaart/fast_math
 https://github.com/RobTillaart/FastMap
 https://github.com/RobTillaart/FastShiftIn