Mention how to remove TreeItem from a Tree

(cherry picked from commit f6aec99d27d2329740b40d7d0f6e06dad564f6e7)

doc/classes/Tree.xml

@@ -16,7 +16,7 @@
 		    var subchild1 = tree.create_item(child1)
 		    subchild1.set_text(0, "Subchild1")
 		[/codeblock]
-		To iterate over all the [TreeItem] objects in a [Tree] object, use [method TreeItem.get_next] and [method TreeItem.get_children] after getting the root through [method get_root].
+		To iterate over all the [TreeItem] objects in a [Tree] object, use [method TreeItem.get_next] and [method TreeItem.get_children] after getting the root through [method get_root]. You can use [method Object.free] on a [TreeItem] to remove it from the [Tree].
 	</description>
 	<tutorials>
 	</tutorials>

doc/classes/TreeItem.xml

@@ -5,6 +5,7 @@
 	</brief_description>
 	<description>
 		Control for a single item inside a [Tree]. May have child [TreeItem]s and be styled as well as contain buttons.
+		You can remove a [TreeItem] by using [method Object.free].
 	</description>
 	<tutorials>
 	</tutorials>
@@ -350,7 +351,7 @@
 			<argument index="0" name="child" type="Object">
 			</argument>
 			<description>
-				Removes the given child TreeItem.
+				Removes the given child [TreeItem] and all its children from the [Tree]. Note that it doesn't free the item from memory, so it can be reused later. To completely remove a [TreeItem] use [method Object.free].
 			</description>
 		</method>
 		<method name="select">