Followup on Cubes compatibility testing

Based on the feedback I’ve received, I conclude that the white-screen/crash problem with Cubes is hardware/driver-specific and not very widespread. Since

• this is a hobby project and an experiment, not a Game to be Published,
• the problem looks hard to debug,
• I don't have a variety of machines to test on, and
• I replaced the MacBook Pro in question with a newer model which does not exhibit the same problem,

I have decided not to debug it further at this time. I've added a note about the problem to the documentation, and I’ll instead work on the problems Cubes exhibits on the new machine :-) (such as a speckling of not-the-right-texture-tile at the edges of blocks, and a strange input lag) or adding new features, like more useful saving/persistence, sub-block collision detection, or subworlds.