add version overview to readme

[jakoch]

• add a compact version overview for images
  • image version tag
  • debian + python + jupyter version
  • docker pull command
  • use https://ghcr-badge.egpl.dev/ to display image stats, e.g. size
    • latest version tag: https://ghcr-badge.egpl.dev/jakoch/jupyter-devbox/latest_tag?trim=major&label=latest&ignore=sha*
    • image size: https://ghcr-badge.egpl.dev/jakoch/jupyter-devbox/size
  • how to get the image stats via api? can we do this on our own - without relying on an external service?