Documentation: hyperv: Add overview of PCI pass-thru device support

Add documentation topic for PCI pass-thru devices in Linux guests
on Hyper-V and for the associated PCI controller driver (pci-hyperv.c).
Signed-off-by: Michael Kelley <mhklinux@outlook.com>
Reviewed-by: Easwar Hariharan <eahariha@linux.microsoft.com>
Link: https://lore.kernel.org/r/20240222200710.305259-1-mhklinux@outlook.comSigned-off-by: Wei Liu <wei.liu@kernel.org>
Message-ID: <20240222200710.305259-1-mhklinux@outlook.com>

Documentation/virt/hyperv/index.rst

@@ -10,3 +10,4 @@ Hyper-V Enlightenments
    overview
    vmbus
    clocks
+   vpci