qemu.nsi: Install Sphinx documentation

qemu.nsi: Install Sphinx documentation

The old qemu-doc.html is no longer built, so update the Windows
installer to install the new Sphinx manual sets.

We install all five of the manuals, even though some of them
(notably the user-mode manual) will not be very useful to Windows
users, because skipping some of them would mean broken links
in the top level 'index.html' page.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20200306134751.2572-1-peter.maydell@linaro.org