Update repositories.txt

Arduino library for creating a Metronome.

Author: RobTillaart

repositories.txt

@@ -5644,6 +5644,7 @@ https://github.com/RobTillaart/MCP4261
 https://github.com/RobTillaart/MCP4725
 https://github.com/RobTillaart/MCP9808_RT
 https://github.com/RobTillaart/MHZCO2
+https://github.com/RobTillaart/Metronome
 https://github.com/RobTillaart/millis64
 https://github.com/RobTillaart/MiniMP3
 https://github.com/RobTillaart/MINMAX