Update README.md

README.md

         testID: 'e2e_rules', // optional, used to locate this view in end-to-end tests
         disabled: true, // optional, used to disable the button (appears faded and doesn't interact)
         disableIconTint: true, // optional, by default the image colors are overridden and tinted to navBarButtonColor, set to true to keep the original image colors
+        showAsAction: 'ifRoom' // optional, Android only. Control how the button is displayed in the Toolbar. Accepted valued: 'ifRoom' (default) - Show this item as a button in an Action Bar if the system decides there is room for it. 'always' - Always show this item as a button in an Action Bar. 'withText' - When this item is in the action bar, always show it with a text label even if it also has an icon specified. 'never' - Never show this item as a button in an Action Bar.
       },
       {
         icon: require('../../img/navicon_add.png'), // for icon button, provide the local image asset name