add popper.js

public/vendor/popper.js/docs/_includes/example50-code.html

@@ -0,0 +1,11 @@
+<h2 id="example5" tabindex="0">Viewport boundaries</h2>
+<p>
+    By default, poppers use as boundaries the page viewport.<br>
+    Scroll the page to see the popper flip when hits the page viewport margins.
+</p>
+
+{% highlight javascript %}
+var popper = new Popper(referenceElement, onBottomPopper, {
+    placement: 'bottom'
+});
+{% endhighlight %}