Clarify the required child node type in the GridContainer documentation

This closes #41822.

(cherry picked from commit 40b5331d794e16c586b9bb5a10a6d820e16be2dc)

doc/classes/GridContainer.xml

@@ -1,11 +1,12 @@
 <?xml version="1.0" encoding="UTF-8" ?>
 <class name="GridContainer" inherits="Container" version="3.2">
 	<brief_description>
-		Grid container used to arrange elements in a grid like layout.
+		Grid container used to arrange Control-derived children in a grid like layout.
 	</brief_description>
 	<description>
-		Grid container will arrange its children in a grid like structure, the grid columns are specified using the [member columns] property and the number of rows will be equal to the number of children in the container divided by the number of columns. For example, if the container has 5 children, and 2 columns, there will be 3 rows in the container.
+		GridContainer will arrange its Control-derived children in a grid like structure, the grid columns are specified using the [member columns] property and the number of rows will be equal to the number of children in the container divided by the number of columns. For example, if the container has 5 children, and 2 columns, there will be 3 rows in the container.
 		Notice that grid layout will preserve the columns and rows for every size of the container, and that empty columns will be expanded automatically.
+		[b]Note:[/b] GridContainer only works with child nodes inheriting from Control. It won't rearrange child nodes inheriting from Node2D.
 	</description>
 	<tutorials>
 	</tutorials>
@@ -13,7 +14,7 @@
 	</methods>
 	<members>
 		<member name="columns" type="int" setter="set_columns" getter="get_columns" default="1">
-			The number of columns in the [GridContainer]. If modified, [GridContainer] reorders its children to accommodate the new layout.
+			The number of columns in the [GridContainer]. If modified, [GridContainer] reorders its Control-derived children to accommodate the new layout.
 		</member>
 		<member name="mouse_filter" type="int" setter="set_mouse_filter" getter="get_mouse_filter" override="true" enum="Control.MouseFilter" default="1" />
 	</members>