More helpful message when TOWN is not present

[SaxxonPike]

When the emulation first starts, it attempts to load TOWN. However, TOWN is not distributed (and will not be distributed) with the binary release of Lyon/Roton. Therefore, the second thing that a user will see is the "DOS Error" scroll.

It might be a good idea to include some kind of fallback world, or display a more helpful message to let the user know that they will need to get some more ZZT worlds.