Update App.tsx (facebook#5588)

Author: brunolemos

packages/react-scripts/template-typescript/src/App.tsx

@@ -9,7 +9,7 @@ class App extends Component {
         <header className="App-header">
           <img src={logo} className="App-logo" alt="logo" />
           <p>
-            Edit <code>src/App.js</code> and save to reload.
+            Edit <code>src/App.tsx</code> and save to reload.
           </p>
           <a
             className="App-link"