add a line space above title

Author: adguernier

docs/Datagrid.md

@@ -1201,6 +1201,7 @@ const MyCustomList = () => {
     );
 };
 ```
+
 ## How to disable checkboxes
 You can disable bulk actions altogether by passing `false` to the `bulkActionButtons` prop. In this case, the checkboxes column doesn’t show up anymore.