How to use pre-built Vanilla UI Extension with Markdown field

The pre-built Vanilla UI Extension available on the “Add extension” > “Install an example” basically allow you to leave a note on the bottom of the input field, so that users can read it.

My intention:
To add a message/sticky note to all our Markdown sections for our web content editors, with instructions (like how to add a clickable link/phone number), and also a link to a specific documentation for detailed instructions.

My challenge:
I don’t know how to use the extension together with the Markdown editor. It seems like I can only select one or the other.

My question is: is it possible to use the extension with Markdown? Or is there another way to add a sticky note to the bottom of a Markdown input field?