Update repositories.txt (#3284)

Arduino library for SWSerialOut, supports only data out (TX).

Author: RobTillaart

repositories.txt

@@ -1750,6 +1750,7 @@ https://github.com/RobTillaart/SHT31_SWW
 https://github.com/RobTillaart/SHT85
 https://github.com/RobTillaart/SIMON
 https://github.com/RobTillaart/SRF05
+https://github.com/RobTillaart/SWSerialOut
 https://github.com/RobTillaart/ShiftInSlow
 https://github.com/RobTillaart/ShiftOutSlow
 https://github.com/RobTillaart/Soundex