Update README.markdown flashing instructions.

README.markdown

@@ -131,6 +131,8 @@ Using avrdude directly:
     avrdude -p x256a3u -c flip2 -U application:w:dstat-firmware.elf:e
 ````
 
+To boot back into the normal DStat firmware, replug the USB without the switch depressed.
+
 Note, DFU flashing will only work if the DFU bootloader is installed and can't be used to set flash bits or flash a new bootloader.
 Unfortunately the XMega doesn't come with a bootloader installed, so flashing with a PDI programmer must be done for at least the first time.