Update repositories.txt (#4905)

Add audio-tools library

Author: egnor

repositories.txt

@@ -4787,6 +4787,7 @@ https://github.com/Protocentral/protocentral-ads1292r-arduino
 https://github.com/Protocentral/protocentral-ads1293-arduino
 https://github.com/Protocentral/protocentral-afe4490-arduino
 https://github.com/Protocentral/protocentral-pulse-express
+https://github.com/pschatzmann/arduino-audio-tools
 https://github.com/pseudoVella/shift7seg
 https://github.com/pstolarz/CoopThreads
 https://github.com/pstolarz/NRF_HAL