docs: ntsync: Add documentation for the ntsync uAPI.

Add an overall explanation of the driver architecture, and complete and precise
specification for its intended behaviour.

Signed-off-by: Elizabeth Figura <zfigura@codeweavers.com>
Link: https://lore.kernel.org/r/20241213193511.457338-30-zfigura@codeweavers.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>