Release criteria proposal: USB-written images

[Petr Schindler]

> As two people voted for it, patch. Beta proposal is unchanged. For
> Alpha, instead of adding a new criterion, the existing criterion is
> simply modified to:
> 
> * The installer must boot (if appropriate) and run on all primary
> architectures, with all system firmware types that are common on those
> architectures, from default live image, DVD, and boot.iso install media
> when written to an optical disc and when written to a USB stick with at
> least one of the [[How_to_create_and_use_Live_USB|officially supported
> methods]]
> 
> It's a bit of an ugly long sentence, but I can't see a way to contract
> it without losing significance, and the two people who commented
> preferred one really long criterion to two quite long ones.

+1 It is long, but understandable.