adding upgrade wiki page to documentation

src/_includes/new-upgrading.html

@@ -0,0 +1,8 @@
+<section id="new-upgrading">
+  <h2 class="page-header">Upgrading from 3.2.1?</h2>
+  <p>
+    <a href="https://twitter.com/gtagliala">@gtagliala</a> has put together a
+    <a href="{{ site.fontawesome.github.url }}/wiki/Upgrading-from-3.2.1-to-4">great wiki page</a> that summarizes the
+    changes in 4.0 syntax and maps the old icon names to the new icon naming conventions.
+  </p>
+</section>

src/whats-new.html

@@ -13,5 +13,6 @@ relative_path: ../
 <div class="container">
   {% include new-features.html %}
   {% include new-naming.html %}
+  {% include new-upgrading.html %}
   {% include icons/new.html %}
 </div>