From: John Arbuckle <programmingkidx@gmail.com>

qemu-doc.texi: Add information on compiling source code on Mac OS X

Add information to the documentation on how to build QEMU
on Mac OS X.

Signed-off-by: John Arbuckle <programmingkidx@gmail.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
[PMM: fixed a minor capitalization error]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>