Added missing login text in jsx

Login text added as child. 
Transpiled code has 'Login' as child but jsx code didn't have 'Login'

Author: ibk6

README.md

@@ -396,7 +396,7 @@
 
     ```javascript
     const Button = ({ onLogin }) =>
-      <div id={'login-btn'} onClick={onLogin} />
+      <div id={'login-btn'} onClick={onLogin}>Login</div>
     ```
 
     Then JSX gets transpiled to a `React.createElement()` function tree: