Clarify sizing of main screen plugins

doc/classes/EditorInterface.xml

@@ -87,6 +87,7 @@
 			<return type="VBoxContainer" />
 			<description>
 				Returns the editor control responsible for main screen plugins and tools. Use it with plugins that implement [method EditorPlugin._has_main_screen].
+				[b]Note:[/b] This node is a [VBoxContainer], which means that if you add a [Control] child to it, you need to set the child's [member Control.size_flags_vertical] to [constant Control.SIZE_EXPAND_FILL] to make it use the full available space.
 				[b]Warning:[/b] Removing and freeing this node will render a part of the editor useless and may cause a crash.
 			</description>
 		</method>

doc/classes/EditorPlugin.xml

@@ -334,7 +334,7 @@
 			<return type="bool" />
 			<description>
 				Returns [code]true[/code] if this is a main screen editor plugin (it goes in the workspace selector together with [b]2D[/b], [b]3D[/b], [b]Script[/b] and [b]AssetLib[/b]).
-				When the plugin's workspace is selected, other main screen plugins will be hidden, but your plugin will not appear automatically. It needs to be added as a child of [method EditorInterface.get_base_control] and made visible inside [method _make_visible].
+				When the plugin's workspace is selected, other main screen plugins will be hidden, but your plugin will not appear automatically. It needs to be added as a child of [method EditorInterface.get_editor_main_screen] and made visible inside [method _make_visible].
 				Use [method _get_plugin_name] and [method _get_plugin_icon] to customize the plugin button's appearance.
 				[codeblock]
 				var plugin_control