Add DietSerial (#6998)

lbrary for ATmega328P Arduinos.

Author: gvp-257

repositories.txt

@@ -8365,6 +8365,7 @@ https://github.com/salesiopark/Chaino.git
 https://github.com/jaikulk14/DataLinkSerial
 https://github.com/tomorrow56/ESPNowAutoPairing
 https://github.com/yohanna02/ESPComm
+https://github.com/gvp-257/DietSerial
 https://github.com/gvp-257/SendOnlySerial
 https://github.com/gvp-257/AnalogControlPanel
 https://github.com/gvp-257/AVRactivePower