Allow markdown in index.yml description field

There is apparently a way to add links in index.yml description, but no success so far:

```
title: Page title
imgSrc:
description: |
[Can this be a link](https://mockbin.org/)
or an image ?
```


Possibly adding HTML to description is a workaround now?

Start by reproducing the example in index.yml and tracing how the CLI parses and renders its description field. Check whether existing documentation or tests cover description formatting. Done means links and images written with Markdown render correctly without breaking plain-text descriptions.

Written by the indexing model from the issue text.