Ubuntu version in tag

### Comment:

Hello,

These images are extremely helpful but it is a bit tricky to understand what underlying ubuntu version is in the corresponding image. I know it can be found, but what would you say in adding it to the tag for clarity somehow? That would make things much more clear!

Second best, would be to have releases in the repo so it is easy to find the version of the Dockerfile (and the ubuntu image) used on a particular tag.

Thank you very much!