Add note about trying to restart Windows if balenaEtcher doesn't start
Observed during Training 1 in Brazil (#19103 (closed)) by a participant with Windows 10 Pro.
Windows 10 asked them to confirm with a security warning, but then nothing happened and balenaEtcher wouldn't start.
They restarted Windows and it worked.
The section about starting balenaEtcher in the instructions is pretty clean and it wouldn't hurt much to add a note about this.