It was explained in the Comments section of Kickstarter Update #43 - see here:
https://www.kickstarter.com/project...1976632?cursor=17903465#comment-17903464(my opinion: Larian should have emailed such important changes to all backers, instead of them being hidden somewhere deep in the comments section... just as they should probably have, at release, sent an email to all Kickstarter backers explaining how they could get their digital game key... even now this is still an FAQ in the Kickstarter comments section)
