fix: README video link improv.

Author: dpc

README.md

@@ -31,7 +31,7 @@ social-graph-based data model.
 
 [<img src="https://img.youtube.com/vi/KjUVKUOg4aE/maxresdefault.jpg" alt="Introduction to Rostra" />](https://www.youtube.com/watch?v=KjUVKUOg4aE)
 
-*▶ Watch on YouTube*
+*[▶ Watch on YouTube](https://www.youtube.com/watch?v=KjUVKUOg4aE)*
 
 ## Using