fix the demo

Author: alexdebril

demo.markdown

@@ -18,6 +18,8 @@ Scans a website and outputs the feeds it provides.
 <input type="url" name="feedToRead" id="feedToRead" />
 <button name="submit" onclick="readFeed()">read</button>
 
+<div id="read-result"></div>
+
 <img src="https://feed-io-api.herokuapp.com" width="0" height="0"/>
 
 <script src="https://unpkg.com/react@16/umd/react.production.min.js" crossorigin></script>

index.markdown

@@ -6,6 +6,7 @@ layout: default
 
 [feed-io](https://github.com/alexdebril/feed-io) is a PHP library built to consume and serve RSS / Atom feeds.
 
+Here's an [online demo](/demo/) of discovering and consuming feeds.
 ```php
 <?php
 require 'vendor/autoload.php';