Check that images have alt text

We use rumdl to lint our markdown, and it has [rule](https://github.com/rvben/rumdl/blob/main/docs/RULES.md) MD045 to yell at us if we forget alt text for images.

We must enable it in our CI.

Read rumdl's MD045 rule documentation, then locate the CI configuration that runs rumdl and check how its rules are enabled. Done means CI checks markdown images for missing alt text and accepts images that include it.

Written by the indexing model from the issue text.