Add comment to distro version field

What does this MR do and why?

I just noticed that Use correct attribute for distro_version (!137309 - merged) did not add the comment suggested in the implementation plan. This MR adds the comment, which I feel is helpful in explaining the behaviour.

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

Before	After

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.