gh-pages: Add `playground` link to homepage. (#26552)

* Add `playground` link

* use `node playground` title

* Update index.html

---------

Co-authored-by: Michael Herzog <[email protected]>

index.html

@@ -48,6 +48,7 @@
 						<li><a href="docs/index.html#manual/introduction/Creating-a-scene">documentation</a></li>
 						<li><a href="examples/#webgl_animation_keyframes">examples</a></li>
 						<li><a href="editor/">editor</a></li>
+						<li><a href="playground/">node editor</a></li>
 					</ul>
 
 					<h2>Community</h2>