docs(templates): add video to unity (#2012)

docs/pages/templates/unity.mdx

@@ -4,4 +4,16 @@
 The Emergence team has built [an open source Unity/MUD integration](https://github.com/emergenceland/UniMUD).
 If you have any questions, you can ask them [in the Emergence Discord](https://discord.com/invite/xbqt42vKJ5).
 
+Watch this tutorial to learn more:
+
+<iframe
+  width="560"
+  height="315"
+  src="https://www.youtube.com/embed/-cRTlDlTmSU?si=EwWriCXP9ZxZJ3-U"
+  title="YouTube video player"
+  frameborder="0"
+  allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share"
+  allowfullscreen
+></iframe>
+
 Disclaimer: We appreciate the team that created this integration, but as we did not verify them ourselves, we cannot guarantee its functionality or security.