Add example for Cytron Maker Pi Pico base

[richsad]

sd_read_simpletest.py.zip
This is a version of the CircuitPython sd_read_sdcard.py example program that I have added instructions on how to read SD card on Cython Maker Pi Pico (which I bought from Adafruit). I have tested this code on a RPi running:

(sysname='rp2040', nodename='rp2040', release='7.3.0', version='7.3.0-beta.2 on 2022-04-27', machine='Raspberry Pi Pico with rp2040')

with RPi Pico plugged into the Cytron Maker Pico base purchased from this page: https://www.adafruit.com/product/5160

Perhaps you would consider adding this change? Thanks for reading

[ladyada]

hi, please submit a PR to add this example, you can label it so its clear its for the maker pi pico