platform/x86: wmi: Add driver development guide

Since 2010, an LWN article covering WMI drivers exists:

https://lwn.net/Articles/391230/

Since the introduction of the modern bus-based interface
and other userspace tooling (bmfdec, lswmi, ...), this
article is outdated and causes people to still submit new
WMI drivers using the deprecated GUID-based interface.
Fix this by adding a short guide on how to develop WMI drivers
using the modern bus-based interface.

Signed-off-by: Armin Wolf <W_Armin@gmx.de>
Link: https://lore.kernel.org/r/20240402143059.8456-4-W_Armin@gmx.de
Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>