Documentation: Add release number to Downloads page

[hseg]

Is your feature request related to a problem? Please describe.
When opening #1446, I noticed the release number under consideration appears nowhere, so my explanation of the situation is unclear. It would make communication clearer if I could cite a version number.

Describe the solution you'd like
On the Downloads page (and in the links to the download images), add the release number of the images.

Describe alternatives you've considered
None -- did consider that one reason not to version is to avoid miscommunicating the message that the images need to be updated on each new release of the distros, but that seemed an insufficient reason to me

Additional context
This is in contrast to any other project I've encountered, was surprised when I realised this was the case.