Added screenshot

README.md

@@ -39,7 +39,7 @@ this Markdown block:
 
 Zefyr can deliver exactly that:
 
-[screenshot]
+![markdown_semantics](/markdown-semantics.png | width=100)
 
 > Nested blocks support (e.g. lists inside quote blocks) is planned.
 

packages/zefyr/example/lib/main.dart

@@ -29,6 +29,7 @@ class ZefyrApp extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     return new MaterialApp(
+      debugShowCheckedModeBanner: false,
       title: 'Zefyr Editor',
       theme: new ThemeData(primarySwatch: Colors.cyan),
       home: new MyHomePage(),