Added react example

step1-04/src/components/Counter.tsx

@@ -0,0 +1,25 @@
+import React from 'react';
+import { Button } from './Button';
+
+export class Counter extends React.Component<any, any> {
+  constructor(props) {
+    super(props);
+    this.state = {
+      counter: props.start
+    };
+  }
+  render() {
+    return (
+      <div>
+        <span> {this.state.counter} </span>
+        <Button
+          onClick={() => {
+            this.setState({ counter: this.state.counter + 1 });
+          }}
+        >
+          Click Me
+        </Button>
+      </div>
+    );
+  }
+}