add recording for EasyBuild webinar (+ trivial update of slides)

Author: boegel

docs/training/2025/EESSI-webinars-MayJune-2025-001-Introduction-to-EasyBuild-20250519.pdf

@@ -146,7 +146,11 @@ hands-on demos. We will also cover some new capabilities that are supported by t
 #### Materials
 
 - [slides (PDF)](EESSI-webinars-MayJune-2025-001-Introduction-to-EasyBuild-20250519.pdf)
-- recording *(coming soon)*
+- [recording (YouTube)](https://www.youtube.com/watch?v=p0Z-KrBAtuQ)
+
+<div align="center">
+<iframe width="560" height="315" src="https://www.youtube.com/embed/p0Z-KrBAtuQ?si=ln66FGzbgZSpoj_H" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share" referrerpolicy="strict-origin-when-cross-origin" allowfullscreen></iframe>
+</div>
 
 ---