Add FastRGB library (#7149)

* Update repositories.txt

* Update repositories.txt

Author: benjistokman

repositories.txt

@@ -8532,5 +8532,6 @@ https://github.com/TamsinRose/CAN_Message_Arduino
 https://github.com/stm32duino/X-NUCLEO-IKS5A1
 https://github.com/fermeridamagni/arduino-minimal-ultrasonic
 https://github.com/chipnorm/TM1637
+https://github.com/benjistokman/FastRGB
 https://github.com/DavinderHanda/HandaDigitalSpeaker
 https://github.com/chipnorm/SHT21