Clarify when to plug USB stick in infography

During #18784 (closed), P1 plugged the USB stick straight away and then got into troubles (eg. #19181 (closed)).

We should clarify in the infography went to plug the USB stick.

Manual upgrades

Similar question was raised for manual upgrades in a mail to tails-bugs@:

• When should the intermediary USB stick be plugged in on https://tails.boum.org/upgrade/tails/#download