Add submission # 6668

#6668

Author: ArduinoBot

registry.txt

@@ -8273,3 +8273,4 @@ https://github.com/dayatkun01/ClearDS1302.git|Contributed|ClearDS1302
 https://github.com/ennio64/CL57R-Stepper-Driver-Arduino-Library.git|Contributed|CL57RStepper
 https://github.com/senex-code/CarBase.git|Contributed|CarBase
 https://github.com/m5stack/M5Unit-Step16.git|Contributed|M5UnitStep16
+https://github.com/Zefek/MQTTESP8266.git|Contributed|MQTTESP8266