Add note regarding supported versions of MinGW
Add note regarding supported versions of MinGW

The original MinGW32 is not supported, due to its
lack of fseeko/ftello.

Signed-off-by: Derek Buitenhuis <aff7d637ede26ea82e5226e01b697996cc52e526@gmail.com>

dwbuiten/d2vsource,dwbuiten/d2vsource