Add notes for a short introduction to NBD.

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+Quick Introduction to NBD
+[About 2 mins 30 seconds]
+
+* Heading: Linux 2.1.55 (1997)
+- Diagram showing two machines
+- Physical disk attached to one
+- Exported to /dev/nbd0 on the other
+- NBD_CMD_READ (0) or NBD_CMD_WRITE (1) only
+
+Network Block Device is a protocol for exporting a disk from
+one machine to another over a network.  It was added to
+Linux 2.1.55 in 1997 and started off very simple with just two commands.
+
+* Heading: Linux 5 (2019)
+- Same diagram annotated with additional commands:
+- DISC, FLUSH, TRIM, CACHE, WRITE_ZEROES, BLOCK_STATUS, RESIZE
+
+In 2019 NBD is quite a bit more complicated, but still
+overall a simple protocol.
+
+* Heading: Exporting a point in time snapshot over NBD
+- Diagram showing qemu exporting a point in time snapshot of a live guest
+- blockdev-backup device=A target=Target sync=none job-id=job1
+- nbd-server-start addr={"type":"unix","data":{"path":"./nbd-sock"}}
+- nbd-server-add device=Target
+
+Our use of NBD today is quite a bit different from how it was
+intended back in 1997.  Here are some ways we're using it today.
+
+As a way to export a point in time snapshot from qemu.
+
+* Heading: Virt-v2v using nbdkit to read a VDDK disk
+- Diagram showing virt-v2v + nbdkit + vddk + VMware
+
+As a way to read a VDDK disk and convert it to run on KVM.
+
+* Heading: qemu-nbd as a high performance server
+- Diagram showing qemu-nbd used by RHV ImageIO
+
+As a high performance server, serving qcow2 files for ImageIO.
+
+* Heading: qemu-img convert from RHV ImageIO to KubeVirt
+- Diagram showing nbdkit -> qemu-img convert -> nbdkit
+
+Copying disk images efficiently between KVM-based management systems.
+
+* Heading: nbdkit linuxdisk used to boot remote machines
+- Diagram showing linuxdisk synthesizing an initramfs/filesystem
+
+Using it as a replacement for TFTP when PXE-booting machines
+over the network.
+
+* Heading: Making disk images for testing
+- Diagram showing an nbdkit shell script plugin
+
+As a general purpose tool to make disk images for testing.
+
+You can think of NBD as a universal protocol that you can use
+whenever you need to access a virtual machine disk, disk image,
+or block device between two processes, whether or not the
+processes are running on the same machine.