Document Timer autostart in tool scripts

doc/classes/Timer.xml

@@ -42,7 +42,7 @@
 	<members>
 		<member name="autostart" type="bool" setter="set_autostart" getter="has_autostart" default="false">
 			If [code]true[/code], the timer will start immediately when it enters the scene tree.
-			[b]Note:[/b] After the timer enters the tree, this property is automatically set to [code]false[/code].
+			[b]Note:[/b] After the timer enters the tree, this property is automatically set to [code]false[/code]. If the timer will be the part of the scene currently opened in the editor (for example, adding and running timer from [code]@tool[/code] script), this property will not set to [code]false[/code] and the timer will not start immediately when it enters the scene tree.
 		</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 after reaching the end. Otherwise, as by default, the timer will automatically restart.