feat: add share to LinkedIn button in final README (#63)

Co-authored-by: Copilot <[email protected]>

Author: FidelusAleksander

markdown-templates/readme/exercise-finished.md

@@ -17,6 +17,9 @@
 <a href="https://bsky.app/intent/compose?text={{ encoded_socials_text }}" target="_blank" rel="noopener noreferrer">
   <img src="https://img.shields.io/badge/Share%20on%20Bluesky-0085ff?style=for-the-badge&logo=bluesky&logoColor=white" alt="Share on Bluesky" />
 </a>
+<a href="https://www.linkedin.com/feed/?shareActive=true&text={{ encoded_socials_text }}" target="_blank" rel="noopener noreferrer">
+  <img src="https://img.shields.io/badge/Share%20on%20LinkedIn-0077b5?style=for-the-badge&logo=linkedin&logoColor=white" alt="Share on LinkedIn" />
+</a>
 
 ### 🎯 What's Next?
 **Keep the momentum going!**