Document update spinner never displaying with `--debug-canvas-item-redraw`

doc/classes/EditorSettings.xml

@@ -716,6 +716,7 @@
 			Consider enabling this if you are developing editor plugins to ensure they only make the editor redraw when required.
 			The default [b]Auto[/b] value will only enable this if the editor was compiled with the [code]dev_build=yes[/code] SCons option (the default is [code]dev_build=no[/code]).
 			[b]Note:[/b] If [member interface/editor/update_continuously] is [code]true[/code], the spinner icon displays in red.
+			[b]Note:[/b] If the editor was started with the [code]--debug-canvas-item-redraw[/code] [url=$DOCS_URL/tutorials/editor/command_line_tutorial.html]command line argument[/url], the update spinner will [i]never[/i] display regardless of this setting's value. This is to avoid confusion with what would cause redrawing in real world scenarios.
 		</member>
 		<member name="interface/editor/single_window_mode" type="bool" setter="" getter="">
 			If [code]true[/code], embed modal windows such as docks inside the main editor window. When single-window mode is enabled, tooltips will also be embedded inside the main editor window, which means they can't be displayed outside of the editor window.