Mention that modifying text erases BBCode stacks

doc/classes/RichTextLabel.xml

@@ -420,7 +420,7 @@
 		</member>
 		<member name="text" type="String" setter="set_text" getter="get_text" default="&quot;&quot;">
 			The label's text in BBCode format. Is not representative of manual modifications to the internal tag stack. Erases changes made by other methods when edited.
-			[b]Note:[/b] If [member bbcode_enabled] is [code]true[/code], it is unadvised to use the [code]+=[/code] operator with [code]text[/code] (e.g. [code]text += "some string"[/code]) as it replaces the whole text and can cause slowdowns. Use [method append_text] for adding text instead, unless you absolutely need to close a tag that was opened in an earlier method call.
+			[b]Note:[/b] If [member bbcode_enabled] is [code]true[/code], it is unadvised to use the [code]+=[/code] operator with [code]text[/code] (e.g. [code]text += "some string"[/code]) as it replaces the whole text and can cause slowdowns. It will also erase all BBCode that was added to stack using [code]push_*[/code] methods. Use [method append_text] for adding text instead, unless you absolutely need to close a tag that was opened in an earlier method call.
 		</member>
 		<member name="text_direction" type="int" setter="set_text_direction" getter="get_text_direction" enum="Control.TextDirection" default="0">
 			Base text writing direction.