docs: vfio: hotplug: metion VFIO at hot-plug supported

Add VFIO devices as hot-plug/unplug supported.

Signed-off-by: Egor Lazarchuk <yegorlz@amazon.co.uk>

Author: ShadowCurse

docs/device-hotplug.md

@@ -12,6 +12,7 @@ running microVM without requiring a reboot. Supported device types are:
 - `virtio-block`
 - `virtio-pmem`
 - `virtio-net`
+- `vfio`
 
 ## Prerequisites