Improve the README.md in the downloaded archive

[dido18]

Polish the readme inside the download zip from here https://www.arduino.cc/en/software/#flasher-tool with the steps to prepare the hardware (like https://docs.arduino.cc/tutorials/uno-q/update-image/) and flashing it.

[dlarue]

Make sure you have updated the instructions( https://docs.arduino.cc/tutorials/uno-q/update-image ) so that step 5 is to REMOVE THE JUMP WIRE and step 6 is the old step 5: "Once flashing completes and the tool reports success, power-cycle the board (unplug and re-plug USB) so it boots the new OS."