message: add dfu-util instructions for Linux
diff: @@ -123,7 +123,19 @@ You can use the DfuSe app from ST.
  1. Congratulations your ODrive should now be flashed; you can now quit DfuSeDemo.
  1. Turn off the power to the ODrive and set the DIP switch back to RUN mode.
  -#### MacOS or Linux
  +#### Linux
  +Install `dfu-util`:
  +```text
  +sudo apt install dfu-util
  +```
  +
  +Force DFU mode, as per the instructions above.
  +In the Firmware directory, after finishing building the firmware:
  +```text
  +sudo dfu-util -a 0 -s 0x08000000 -D build/ODriveFirmware.bin
  +```
  +
  +#### MacOS
  **This section needs more detail. Please consider adding detail if you got it to work.**
  You may be able to use [dfu-util](http://dfu-util.sourceforge.net/) to upgrade the firmware. You will need to convert the .hex file to a .dfu file. You may be able to do it with the python script [dfu-convert](https://github.com/plietar/dfuse-tool/blob/master/dfu-convert) or the c program [hex2dfu](https://github.com/encedo/hex2dfu).
  