docs: inline "Simple" demo as CopePen Embed

Author: gruhn

docs/demos/Simple.md

@@ -1,8 +1,14 @@
 # Simple
 
-All demos on this page utilize [single-file components](https://vuejs.org/v2/guide/single-file-components.html).
+All other demos on this page utilize [single-file components](https://vuejs.org/v2/guide/single-file-components.html).
 To use them in your project you need a bundler like webpack.
 
-For simpler example that works without a build step and right in the browser, checkout [this fiddle](https://jsfiddle.net/vqg8to36/1/).
+For simpler example that works without a build step and right in the browser, checkout this:
 
 
+<p class="codepen" data-height="265" data-theme-id="light" data-default-tab="js,result" data-user="gruhn" data-slug-hash="rNxQPay" style="height: 265px; box-sizing: border-box; display: flex; align-items: center; justify-content: center; border: 2px solid; margin: 1em 0; padding: 1em;" data-pen-title="rNxQPay">
+  <span>See the Pen <a href="https://codepen.io/gruhn/pen/rNxQPay">
+  rNxQPay</a> by Niklas (<a href="https://codepen.io/gruhn">@gruhn</a>)
+  on <a href="https://codepen.io">CodePen</a>.</span>
+</p>
+<script async src="https://static.codepen.io/assets/embed/ei.js"></script>