Add demonstration video to docs homepage

Author: Guts

docs/index.md

@@ -10,6 +10,17 @@
 
 ----
 
+<!-- markdownlint-disable MD033 -->
+<video width="100%" controls>
+      <source src="https://user-images.githubusercontent.com/1596222/232868878-1134695b-5dd8-405e-96af-00a2856d4535.webm" type="video/webm">
+      Your browser does not support video tag of HTML5.
+</video>
+<!-- markdownlint-enable MD033 -->
+
+> [Click here to see video demonstration in fullscreen](https://user-images.githubusercontent.com/1596222/232868878-1134695b-5dd8-405e-96af-00a2856d4535.webm)
+
+----
+
 ```{toctree}
 ---
 caption: Usage