OK. It wasn't so simple.
Anyway, what is the transmitter going to do ? You haven't got many pins left on the MCU for much other activity. I suppose it could send its own battery voltage back to the receiver and, maybe temperature.
Incidentally, a much nicer pinout diagram can be found here without hunting through .h files: megaTinyCore/ATtiny_x12.md at master · SpenceKonde/megaTinyCore · GitHub
