[3.x] Document Timer autostart in tool scripts

(cherry picked from commit 0e674d74f2)

doc/classes/Timer.xml

@@ -37,6 +37,7 @@
 		<member name="autostart" type="bool" setter="set_autostart" getter="has_autostart" default="false">
 			If [code]true[/code], the timer will automatically start when entering the scene tree.
 			[b]Note:[/b] This property is automatically set to [code]false[/code] after the timer enters the scene tree and starts.
+			[b]Note:[/b] This property does nothing when the timer is running in the editor.
 		</member>
 		<member name="one_shot" type="bool" setter="set_one_shot" getter="is_one_shot" default="false">
 			If [code]true[/code], the timer will stop when reaching 0. If [code]false[/code], it will restart.