Review description of image sizes in README

[MikeMcC399]

On a slightly related topic, it seems that the README > Image variants is biased towards Alpine for size considerations where it refers to the base image being ~5 MB, although the final compressed image sizes for alpine and trixie-slim with Node.js and other dependencies added, aren't that much different.

If I had to choose between the unofficial node:25.5-alpine3.23 at 56.63 MB compressed and the official node:25.5-trixie-slim at 76.55 MB compressed, I would choose the trixie-slim variant. I will separate this point into a different issue.

Originally posted by @MikeMcC399 in #2011