Documentation: Describe NBD URL syntax

This patch adds a short description of how to specify a NBD device
to QEMU.
Syntax for both TCP and Unix Domain Sockets are provided as well
as examples.

Signed-off-by: Ronnie Sahlberg <ronniesahlberg@gmail.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
diff --git a/qemu-options.hx b/qemu-options.hx
index 424bae9..c55080c 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -1757,6 +1757,27 @@
 iSCSI support is an optional feature of QEMU and only available when
 compiled and linked against libiscsi.
 
+@item NBD
+QEMU supports NBD (Network Block Devices) both using TCP protocol as well
+as Unix Domain Sockets.
+
+Syntax for specifying a NBD device using TCP
+``nbd:<server-ip>:<port>[:exportname=<export>]''
+
+Syntax for specifying a NBD device using Unix Domain Sockets
+``nbd:unix:<domain-socket>[:exportname=<export>]''
+
+
+Example for TCP
+@example
+qemu --drive file=nbd:192.0.2.1:30000
+@end example
+
+Example for Unix Domain Sockets
+@example
+qemu --drive file=nbd:unix:/tmp/nbd-socket
+@end example
+
 @end table
 ETEXI