Flagging this for post-europa.

CUE snippets used to be external to markdown files, like so:

```cue file=./tests/cloudformation/template.cue title="todoapp/cloudformation/template.cue"
``

This allows:

1. CUE linter cleaning up the files / validating them
2. Adding automated tests using the snippets, to make sure the docs work

I think I've seen a couple of embedded CUE snippets in the latest Europa markdowns (/cc @gerhard @helderco)