Added DOS floppy disk image

I added a DOS floppy disk image with a simple installer. If you want to play the game on a retro Pentium (preferably 200MHz or above) PC running DOS (or through a full PC emulator like 86box or PCem) you can use this floppy disk image instead of the ZIP files for a more authentic experience :-P.

Note that this version contains only the DOS executables - use the ZIP file if you also want the Windows executables.