docs(readme): Update design

Author: julienloizelet

README.md

@@ -1,13 +1,14 @@
 # DDEV add-on test action
 
+---
 > A GitHub action to run tests on a DDEV add-on.
+---
 
 [![Version](https://img.shields.io/github/v/release/ddev/github-action-add-on-test)](https://github.comddev/github-action-add-on-test/releases)
 ![project is maintained](https://img.shields.io/maintenance/yes/2024.svg)
 [![tests](https://github.com/ddev/github-action-add-on-test/actions/workflows/single-add-on-test.yml/badge.svg)](https://github.com/ddev/github-action-add-on-test/actions/workflows/single-add-on-test.yml)
 
 
-
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 **Table of Contents**