Update repositories.txt (arduino#2869)

Add TOPMIN, an Arduino library to track top N minima.

Author: RobTillaart

repositories.txt

@@ -1653,6 +1653,7 @@ https://github.com/RobTillaart/TCA9548
 https://github.com/RobTillaart/TCA9555
 https://github.com/RobTillaart/TM1637_RT
 https://github.com/RobTillaart/TOPMAX
+https://github.com/RobTillaart/TOPMIN
 https://github.com/RobTillaart/TSL235R
 https://github.com/RobTillaart/TSL260R
 https://github.com/RobTillaart/Temperature