chore: Add deprecation notice in header.

Author: chriswblake

README.md

@@ -1,5 +1,9 @@
 <header>
 
+![Deprecation Badge](https://img.shields.io/badge/Skills-Deprecated-333?logo=github&labelColor=454c54&color=bf8700)
+
+This course has been deprecated. Please visit the [Getting Started with GitHub Copilot](https://github.com/skills/getting-started-with-github-copilot) exercise for the newest learning content.
+
 <!--
   <<< Author notes: Course header >>>
   Read <https://skills.github.com/quickstart> for more information about how to build courses using this template.