Merge pull request #10540 from bpasero/touchbar-docs

Docs: set iconPosition as optional

docs/api/touch-bar-button.md

@@ -11,7 +11,7 @@ Process: [Main](../tutorial/quick-start.md#main-process)
   * `backgroundColor` String (optional) - Button background color in hex format,
     i.e `#ABCDEF`.
   * `icon` [NativeImage](native-image.md) (optional) - Button icon.
-  * `iconPosition` String - Can be `left`, `right` or `overlay`.
+  * `iconPosition` String (optional) - Can be `left`, `right` or `overlay`.
   * `click` Function (optional) - Function to call when the button is clicked.
 
 ### Instance Properties