Update Docker Hub pull stats in README.md

[jfpanisset]

The README.md shows badges for Docker Hub pull stats, but is somewhat misleading since it implies that the counts are per version / tag, whereas they are for all tags. The README.md should be reformatted to move the counter under the global header for the image, not the per version one.

Even better would be to have access to finer grained analytics, which may or may not be possible with our current Docker Hub subscription.

https://docs.docker.com/docker-hub/repos/manage/trusted-content/dsos-program/