update compatibility matrix in README

Author: andydoro

README.md

@@ -27,7 +27,7 @@ MCU               | Tested Works | Doesn't Work | Not Tested  | Notes
 Atmega328 @ 16MHz |      X       |             |            | 
 Atmega328 @ 12MHz |             |      X       |            | 
 Atmega32u4 @ 16MHz |      X       |             |            | 
-Atmega32u4 @ 8MHz |             |             |     X       | 
+Atmega32u4 @ 8MHz |             |      X       |            | 
 ESP8266           |             |             |     X       | 
 Atmega2560 @ 16MHz |             |             |     X       | 
 ATSAM3X8E         |             |             |     X       |