Custom App: Add field like "Help text" to tab "appearance"

I am creating a custom app that is located on a field.

I’ve seen that Slug, Radio… and other fields have a field called “Help text” in the “Appearance” tab. How can I add such a field to my custom app and read out its value inside the custom app?

Someone in the Contentful Slack community pointed me to the solution: App Parameters | Contentful