add popper.js

public/vendor/popper.js/docs/_includes/example40-code.html

@@ -0,0 +1,14 @@
+<h2 id="example4" tabindex="0">Shifted poppers</h2>
+<p>
+    Shift your poppers on start or end of its reference element side.
+</p>
+
+{% highlight javascript %}
+var shiftStart = new Popper(referenceElement, shiftStartPopper, {
+    placement: 'left-start',
+});
+
+var shiftEnd = new Popper(referenceElement, shiftEndPopper, {
+    placement: 'bottom-end',
+});
+{% endhighlight %}