add credit to where credit is due :)

Author: brentru

adafruit_esp32spi/digitalio.py

@@ -24,7 +24,10 @@
 ==============================
 DigitalIO for ESP32 over SPI.
 
-* Author(s): Brent Rubell
+* Author(s): Brent Rubell, based on Adafruit_Blinka digitalio implementation
+and bcm283x Pin implementation.
+https://github.com/adafruit/Adafruit_Blinka/blob/master/src/adafruit_blinka/microcontroller/bcm283x/pin.py
+https://github.com/adafruit/Adafruit_Blinka/blob/master/src/digitalio.py
 """
 from micropython import const