release_process: robustify boot profile instructions
Originally created by @CyrilBrulebois on #16582 (Redmine)
We have automated USB repartitioning and we switched to boot profiling USB images… I suppose it would be good to document explicitly that one should copy the reference image again in case boot profiling didn’t work the first time around, as the repartitioning step could interfere somewhat? (E.g. if that’s been doing one the first boot already, then skipped on the second one.)