docs: update README to include a dedicated demo video section with a larger thumbnail.

Author: alepot55

README.md

@@ -9,9 +9,16 @@
     <a href="#testing"><img src="https://img.shields.io/badge/tests-421%2B-blue.svg" alt="421+ Tests"></a>
     <a href="LICENSE"><img src="https://img.shields.io/badge/license-MIT-green.svg" alt="MIT License"></a>
   </p>
-  <p align="center">
-    <a href="https://youtu.be/2Tv3cGaI6PM"><img src="https://img.shields.io/badge/▶_Demo_Video-YouTube-red.svg" alt="Demo Video"></a>
-  </p>
+</p>
+
+---
+
+## Demo Video
+
+<p align="center">
+  <a href="https://youtu.be/2Tv3cGaI6PM">
+    <img src="https://img.youtube.com/vi/2Tv3cGaI6PM/maxresdefault.jpg" alt="verify-cbl Demo Video" width="600">
+  </a>
 </p>
 
 ---