Update repositories.txt (#2505)

This is a fork of the main repository, which was last updated in 2020.
Since we have an SDK based on this client, we decided to continue with this library.
We also believe that this library provides a lot of opportunities for people who want to build their own IoT devices.

Author: imbeacon

repositories.txt

@@ -4387,6 +4387,7 @@ https://github.com/thingface/arduino
 https://github.com/ThingPulse/esp8266-oled-ssd1306
 https://github.com/ThingPulse/XPT2046_Touchscreen
 https://github.com/thingsboard/ThingsBoard-Arduino-SDK
+https://github.com/thingsboard/pubsubclient
 https://github.com/thingSoC/embedis
 https://github.com/thinkovation/Ambimate
 https://github.com/ThisSmartHouse/CoogleIOT