clarify wording on troubleshooting instructions

[spookyvision]

in hello board it says

1. press and hold boot button on the board, start flash command, release boot button after flashing process starts

Context: sometimes (see context in #109) the firmware update tool fails to put the board in firmware upload mode, for reasons currently not 100% clear. The solution is to

1. press and hold boot
2. press and release reset
3. release boot
4. start a firmware build+upload (e.g. cargo espflash --release) and wait for it to complete (adding --monitor will not cause any harm but also not give any real benefits since you'll just be greeted with a waiting for download message)
5. press reset once more (without holding the boot button)
6. manually connecting to the serial via espmonitor <device>