Move vmm examples doc here from the LionsOS tree.

Signed-off-by: Peter Chubb <Peter.Chubb@unsw.edu.au>

content/docs/examples/vmm/_index.md

@@ -0,0 +1,82 @@
+Simple VM with passthrough
+================================
+
+This directory contains what's needed to run a complete VM with
+passthrough of all components (including the GPU) on an Odroid C4.
+
+Such a VM can be used to develop new LionsOS components, and is fairly
+easy to adapt to other systems.
+
+What you need
+=================
+
+Build and Source dependencies
+-----------------------------
+
+It's easiest to build if you have a complete checkout of
+[LionsOS](https://github.com/au-ts/LionsOS)
+
+If you follow the instructions at [LionsOS
+Docs](https://lionsos.org/docs/kitty/building/) you will have all the
+prerequisites.
+
+Payload
+-------
+
+You need a kernel, device tree and initrd that work already on your
+target system.  The simplest way to get them is to extract them from
+`/boot` on your system after it is running.
+
+For Armbian-based systems, the files you need are `/boot/Image`
+`/boot/initrd.img` and `/boot/dtb/amlogic/meson-sm1-odroid-c4.dtb`.
+Boot your board into Linux, then use `scp` to transfer these files to
+your build machine, and put them into the `vmm` subdirectory.
+
+The Makefile will fetch some from our website if they are missing from
+`vmm`, but there's no guarantee they'll match what's on your root
+filesystem --- they were taken from an
+[Armbian](https://github.com/armbian/community/releases/download/24.5.0-trunk.168/Armbian_community_24.5.0-trunk.168_Odroidc4_jammy_current_6.6.21_gnome_desktop.img.xz)
+'Jammy' Ubuntu system.
+
+You will also need to update the commandline in `vmm/overlay.dts`,
+especially if you are not running Ubuntu Jammy Armbian.
+
+The Microkit
+------------
+
+You can use the prebuilt microkit from
+[Prebuilt](https://github.com/seL4/microkit/releases/download/1.4.1/microkit-sdk-1.4.1-linux-x86-64.tar.gz)
+
+If you choose to build your own, 
+you can build it by following
+the instructions in the
+[ReadMe](https://github.com/seL4/microkit)
+
+You need version 1.4.1
+
+Building
+--------
+
+You need to have `aarch64-none-elf-gcc` etc., in your PATH; plus you
+need to set the LIONSOS and MICROKIT_SDK environment variables.
+
+If you build from within the LionsOS repository the default LIONSOS
+will work.  You can copy the whole `examples/vmm` directory somewhere
+else, and use it for a complete out-of-tree build if you'd prefer.
+
+```
+MICROKIT_SDK=.../path-to/microkit-sdk-1.4.1 LIONSOS=.../path-to/LionsOS make
+```
+
+If all goes well, a directory called `build`,and a
+bootable image `boot/vmdev.img`, will be created.
+
+There are two variants you can build.  The standard variant passes
+through _everything_; the `virtio_console` variant uses the sDDF's
+UART driver and a virtio console.
+
+To select, do
+```
+make VARIANT=virtio_console MICROKIT_SDK=... ...
+```
+