Codespaces Pre-cached Image List

There does not appear to be any definitive list of which images are pre-cached in Github Codespaces so as to save a download. The universal images readme used to have a note that the latest version was precached.

This info should be added to the README to the file, or, if keeping this agnostic, link to a GitHub article or otherwise that lists what images are pre-cached in codespaces.