docs(brightness-widget): add new options to README

Author: NStefan002

brightness-widget/README.md

@@ -18,6 +18,8 @@ It is possible to customize widget by providing a table with all or some of the
 | `tooltip` | false | Display brightness level in a tooltip when the mouse cursor hovers the widget |
 | `percentage` | false | Display a '%' character after the brightness level |
 | `rmb_set_max` | false | Right mouse click sets the brightness level to maximum |
+| `size` | 18 | Size of the widget (used only for `arc` type) |
+| `arc_thickness` | 2 | Thickness of the arc (used only for `arc` type) |
 
 _Note:_ If brightness is controlled only by the widget (either by a mouse, or by a shortcut, then the `timeout` could be quite big, as there is no reason to synchronize the brightness level).