Update example for more common pins?

[caternuson]

Re this thread:
https://forums.adafruit.com/viewtopic.php?f=60&t=189733

The max7219_simpletest.py example is using board.TX for MOSI, board.RX for SCLK, and board.A1 for CS. Might have been written for a specific board? But there's no associated guide AFAICT, so wiring is only documented by the code. Might be better to use actual SPI pins?