update compatibility matrix in README

Author: andydoro

README.md

@@ -17,3 +17,33 @@ All text above must be included in any redistribution
 To download. click the DOWNLOADS button in the top right corner, rename the uncompressed folder Adafruit_PWMServoDriver. Check that the Adafruit_PWMServoDriver folder contains Adafruit_PWMServoDriver.cpp and Adafruit_PWMServoDriver.h
 
 Place the Adafruit_PWMServoDriver library folder your <arduinosketchfolder>/libraries/ folder. You may need to create the libraries subfolder if its your first library. Restart the IDE.
+
+<!-- START COMPATIBILITY TABLE -->
+
+## Compatibility
+
+MCU               | Tested Works | Doesn't Work | Not Tested  | Notes
+----------------- | :----------: | :----------: | :---------: | -----
+Atmega328 @ 16MHz |      X       |             |            | 
+Atmega328 @ 12MHz |             |             |     X       | 
+Atmega32u4 @ 16MHz |             |             |     X       | 
+Atmega32u4 @ 8MHz |             |             |     X       | 
+ESP8266           |             |             |     X       | 
+Atmega2560 @ 16MHz |             |             |     X       | 
+ATSAM3X8E         |             |             |     X       | 
+ATSAM21D          |             |             |     X       | 
+ATtiny85 @ 16MHz  |             |             |     X       | 
+ATtiny85 @ 8MHz   |             |             |     X       | 
+
+  * ATmega328 @ 16MHz : Arduino UNO, Adafruit Pro Trinket 5V, Adafruit Metro 328, Adafruit Metro Mini
+  * ATmega328 @ 12MHz : Adafruit Pro Trinket 3V
+  * ATmega32u4 @ 16MHz : Arduino Leonardo, Arduino Micro, Arduino Yun, Teensy 2.0
+  * ATmega32u4 @ 8MHz : Adafruit Flora, Bluefruit Micro
+  * ESP8266 : Adafruit Huzzah
+  * ATmega2560 @ 16MHz : Arduino Mega
+  * ATSAM3X8E : Arduino Due
+  * ATSAM21D : Arduino Zero, M0 Pro
+  * ATtiny85 @ 16MHz : Adafruit Trinket 5V
+  * ATtiny85 @ 8MHz : Adafruit Gemma, Arduino Gemma, Adafruit Trinket 3V
+
+<!-- END COMPATIBILITY TABLE -->