Docs/ABI/testing: Add VDUSE sysfs interface ABI document

This adds missing documentation for VDUSE sysfs interface ABI
under Documentation/ABI/testing.

Signed-off-by: Xie Yongji <[e-mail]>
Acked-by: Jason Wang <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

Documentation/ABI/testing/sysfs-class-vduse

···
+What:		/sys/class/vduse/
+Date:		Oct 2021
+KernelVersion:	5.15
+Contact:	Yongji Xie <[e-mail]>
+Description:
+		The vduse/ class sub-directory belongs to the VDUSE
+		framework and provides a sysfs interface for configuring
+		VDUSE devices.
+
+What:		/sys/class/vduse/control/
+Date:		Oct 2021
+KernelVersion:	5.15
+Contact:	Yongji Xie <[e-mail]>
+Description:
+		This directory entry is created for the control device
+		of VDUSE framework.
+
+What:		/sys/class/vduse/<device-name>/
+Date:		Oct 2021
+KernelVersion:	5.15
+Contact:	Yongji Xie <[e-mail]>
+Description:
+		This directory entry is created when a VDUSE device is
+		created via the control device.
+
+What:		/sys/class/vduse/<device-name>/msg_timeout
+Date:		Oct 2021
+KernelVersion:	5.15
+Contact:	Yongji Xie <[e-mail]>
+Description:
+		(RW) The timeout (in seconds) for waiting for the control
+		message's response from userspace. Default value is 30s.
+		Writing a '0' to the file means to disable the timeout.

MAINTAINERS

···
 L:	[e-mail]
 S:	Maintained
 F:	Documentation/ABI/testing/sysfs-bus-vdpa
+F:	Documentation/ABI/testing/sysfs-class-vduse
 F:	Documentation/devicetree/bindings/virtio/
 F:	drivers/block/virtio_blk.c
 F:	drivers/crypto/virtio/