Adding link to Dafny YouTube channel (#47)

index.html

@@ -34,6 +34,7 @@ <h1>The Dafny Programming and Verification Language</h1>
 <li><a href="./latest/DafnyRef/DafnyRef">Reference Manual and User Guide</a></li>
 <li><a href="./latest/toc">Resources for Users</a></li>
 <li><a href="./blog">Blog</a></li>
+<li><a href="https://www.youtube.com/@DafnyVideos" target="_blank">YouTube channel</a></li>
 <li><a href="https://github.com/dafny-lang/dafny">Contribute on GitHub</a></li>
 <li><a href="./Snapshots">Documentation snapshots</a></li>
 <li><a href="https://mitpress.mit.edu/9780262546232/program-proofs"><i>Program Proofs</i>, by Rustan Leino, MIT Press</a></li>