minor readme tweaks

step1-04/demo/src/App.tsx

@@ -0,0 +1,12 @@
+import React from 'react';
+
+export class App extends React.Component {
+  render() {
+    let text = 'My App';
+    return (
+      <div className="App">
+        <h2>{text !== '' ? text : 'Default App Name'}</h2>
+      </div>
+    );
+  }
+}

step1-04/demo/src/components/Counter.tsx

@@ -2,8 +2,6 @@ import React from 'react';
 
 export class Counter extends React.Component {
   render() {
-    return (
-    
-    );
+    return <p>hello</p>;
   }
 }