Adding readme about the firmwares.

Author: damellis

hardware/arduino/firmwares/README.txt

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+Arduino Uno and Mega 2560 Firmwares for the ATmega8U2
+
+This directory contains the firmwares used on the ATmega8U2 on the Arduino
+Uno and Arduino Mega 2560.  The arduino-usbdfu directory contains the DFU
+bootloader on the 8U2; the arduino-usbserial directory contains the actual
+usb to serial firmware.  Both should be compiled against LUFA 100807.  The
+two .hex files in this directory combine the dfu and serial firmwares into
+a single file to burn onto the 8U2.  
+
+To burn (Uno):
+avrdude -p at90usb82 -F -P usb -c avrispmkii -U flash:w:UNO-dfu_and_usbserial_combined.hex -U lfuse:w:0xFF:m -U hfuse:w:0xD9:m -U efuse:w:0xF4:m -U lock:w:0x0F:m
+
+To burn (Mega 2560):
+avrdude -p at90usb82 -F -P usb -c avrispmkii -U flash:w:MEGA-dfu_and_usbserial_combined.hex -U lfuse:w:0xFF:m -U hfuse:w:0xD9:m -U efuse:w:0xF4:m -U lock:w:0x0F:m