add heading class and content class options

6.x/base-widgets.md

@@ -402,9 +402,12 @@ Shows a Bootstrap jumbotron component, with the heading and body you specify.
 [
     'type'        => 'jumbotron',
     'heading'     => 'Welcome!',
-    'content'     => 'Use the sidebar to the left to create, edit or delete content.',
+    'content'     => 'My magnific headline! Lets build something awesome together.',
     'button_link' => backpack_url('logout'),
     'button_text' => 'Logout',
+    // OPTIONAL:
+    'heading_class' => 'display-3 text-white',
+    'content_class' => 'text-white',
 ]
 ```