[physfs] physfs tutorial

[Ryan C. Gordon]

> There was discussion about making Cygwin builds use '/' as a path
> seperator to make them "Unix-like", but I'm not sure I think that's
> right for gamers

(whoops, hit SEND too soon...)

...right for gamers playing on Windows.

Not to mention it'd probably wreak havoc with win32.c. I'm not against a
./configure option for cygwin to build against posix.c+unix.c instead of
win32.c, though.

--ryan.