[DOCS] Node & PackedScene (#17833)

* [DOCS] Node: SceneSaver -> PackedScene

* [DOCS] PackedScene: Code example, resolve TODO

doc/classes/PackedScene.xml

@@ -5,7 +5,14 @@
 	</brief_description>
 	<description>
 		A simplified interface to a scene file. Provides access to operations and checks that can be performed on the scene resource itself.
-		TODO: explain ownership, and that node does not need to own itself
+		Can be used to save a node to a file. When saving, the node as well as all the node it owns get saved (see [code]owner[/code] property on [Node]). Note that the node doesn't need to own itself.
+		Example of saving a node:
+		[codeblock]
+		var scene = PackedScene.new()
+		var result = scene.pack(child)
+		if result == OK:
+		    ResourceSaver.save("res://path/name.scn", scene) // or user://...
+		[/codeblock]
 	</description>
 	<tutorials>
 	</tutorials>