Update README.

examples/docker-cross-compile/README.md

@@ -1,4 +1,22 @@
 # Cross-compilation using Docker
 
-This example uses Docker to cross-compile images to different architectures, in this case, to the Raspberry Pi.
+This example uses Docker to cross-compile to a different architecture, in this case, to the Raspberry Pi. To run this,
 
+```console
+pants package examples/docker-cross-compile::
+```
+
+This will build the docker cross compiler image and then compile the module, with a binary in `dist/examples.docker-cross-compile/hello-cross`. You can then copy this to an ARM64 machine running linux, e.g., a raspberry pi:
+
+```console
+export RPI_USER=username
+export RPI_HOST=raspberry.local
+
+scp -q dist/examples.docker-cross-compile/hello-cross ${RPI_USER}@${RPI_HOST}:/home/${RPI_USER}
+ssh ${RPI_USER}@${RPI_HOST} -t './hello-cross'
+```
+
+You should see an output like
+```
+Successfully compiled for ARM architecture.
+```