Update README.md

Indumathi1195R · web-flow · commit 128c8889b691 · 2020-05-05T12:18:26.000+05:30
diff --git a/README.md b/README.md
@@ -43,7 +43,7 @@ leading: PopupMenuButton<String>(
   },
 ),
 ```
-Step 3:
+## Step 3:
 Place the calendar inside the body of the Scaffold widget.
 
 ```xml
