examples/simple: initial README

examples/simple/README.md

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+# A simple VMM for running Linux guests
+
+This example is a minimal VMM that supports Linux guests and a basic
+buildroot/BusyBox root file system. This gives a basic command-line with some
+utilities.
+
+## Building with Make
+
+```sh
+make BOARD=<BOARD> SEL4CP_SDK=/path/to/sel4cp-sdk-1.2.6
+```
+
+Where `<BOARD>` is one of:
+* `qemu_arm_virt_hyp`
+* `odroidc4_hyp`
+
+Other configuration options can be passed to the Makefile such as `CONFIG`
+and `BUILD_DIR`, see the Makefile for details.
+
+If you would like to simulate the QEMU board you can run the following command:
+```sh
+make BOARD=qemu_arm_virt_hyp SEL4CP_SDK=/path/to/sel4cp-sdk-1.2.6 simulate
+```
+
+This will build the example code as well as run the QEMU command to simulate a
+system running the whole system.
+
+## Building with Zig
+
+For educational purposes, you can also build and run this example using the
+[Zig](https://ziglang.org/) build system.
+
+You will first need Zig version 0.11.0, which can be downloaded here: [TODO]().
+
+```sh
+zig build -Dtarget="aarch64-freestanding" -Doptimize=ReleaseFast simualte
+```