add custom octoprint dockerfile; add link about cross-building images to buildscript

scripts/build-images.sh

@@ -1,5 +1,8 @@
 #!/bin/bash
 
+## https://www.stereolabs.com/docs/docker/building-arm-container-on-x86/
+## docker run --rm --privileged multiarch/qemu-user-static --reset -p yes
+
 set -e
 
 registry=${1}