Clarify is_action_pressed() for multiple assigned buttons

(cherry picked from commit 7e329a7251b603c3d46da2456d687754547c5793)

doc/classes/Input.xml

@@ -217,7 +217,7 @@
 			<argument index="0" name="action" type="String">
 			</argument>
 			<description>
-				Returns [code]true[/code] if you are pressing the action event.
+				Returns [code]true[/code] if you are pressing the action event. Note that if an action has multiple buttons asigned and more than one of them is pressed, releasing one button will release the action, even if some other button assigned to this action is still pressed.
 			</description>
 		</method>
 		<method name="is_joy_button_pressed" qualifiers="const">