Add submission # 6607

#6607

Author: ArduinoBot

registry.txt

@@ -8219,3 +8219,4 @@ https://github.com/boby15000/Tempo.git|Contributed|Tempo
 https://github.com/X-croot/XCR-LDR.git|Contributed|XCR-LDR
 https://github.com/LFranklinApps/Custom_Robot_Control.git|Contributed|Custom_Robot_Control
 https://github.com/npuckett/WebGUI.git|Contributed|WebGUI
+https://github.com/kolod/Arduino-Simple-Modbus-Slave.git|Contributed|SimpleModbusSlave