Add an example of building an application and running in Docker or LinuxKit

Signed-off-by: Justin Cormack <justin.cormack@docker.com>

examples/linuxkit.yml

@@ -0,0 +1,18 @@
+kernel:
+  image: "linuxkit/kernel:4.9.x"
+  cmdline: "console=ttyS0"
+init:
+  - linuxkit/init:1b8a7e394d2ec2f1fdb4d67645829d1b5bdca037
+  - linuxkit/runc:3a4e6cbf15470f62501b019b55e1caac5ee7689f
+  - linuxkit/containerd:5749f2e9e65395cc6635229e8da0e0d484320ddf
+  - linuxkit/ca-certificates:75cf419fb58770884c3464eb687ec8dfc704169d
+onboot:
+  - name: dhcpcd
+    image: "linuxkit/dhcpcd:7d2b8aaaf20c24ad7d11a5ea2ea5b4a80dc966f1"
+    command: ["/sbin/dhcpcd", "--nobackground", "-f", "/dhcpcd.conf", "-1"]
+services:
+  - name: rngd
+    image: "linuxkit/rngd:1fa4de44c961bb5075647181891a3e7e7ba51c31"
+trust:
+  org:
+    - linuxkit