Add submission # 6976

#6976

Author: ArduinoBot

registry.txt

@@ -8417,3 +8417,4 @@ https://github.com/hidori/MicroSerial.git|Contributed|MicroSerial
 https://github.com/gustavofisica/PulseHeartLab.git|Contributed|PulseHeartLab
 https://github.com/7semi-solutions/7Semi-BNO055-Arduino-Library.git|Contributed|7Semi_BNO055
 https://github.com/ConsentiumIoT/EdgeVision.git|Contributed|EdgeVision
+https://github.com/junzzhu/esp-mqtt-arduino.git|Contributed|esp-mqtt-arduino