Well - you can't rewrite the law (just as well, too), and phrases are not legally binding if they are not accepted by both parties, and merely asserting that the user agrees to something doesn't make it so. "Forbidden" is a strong word. You can forbid people to do this, that and the other in a readme file as much as you like, but don't imagine this has legal force. It is better to think of the conditions in a readme as a request, which the user certainly ought to respect (otherwise the donor gets pissed off and goes away). But the conditions of use in a readme file only have real force in so far as they are backed up by existing law. So if you say "Please do not redistribute this file without permission", and someone does, you can get them for copyright violation. But if you put in "This model may not be used in religious artworks", or "It is forbidden to use this file if your first name begins with P", you have no recourse in law at all if someone disregards this.