Update documentation for 3.0

docs/_includes/header.html

@@ -16,7 +16,12 @@
         <a class="page-link" href="{{ site.github.url }}/docs/">Documentation</a>
         <a class="page-link" href="{{ site.github.url }}/guides/">Guides</a>
         <a class="page-link" href="{{ site.github.url }}/faq/">FAQ</a>
-        <a class="page-link" href="https://github.com/box/spout">GitHub</a>
+        <a class="page-link" href="https://github.com/box/spout">
+            GitHub
+            <svg width="12" height="12">
+                <image xlink:href="/images/external-link.svg" src="/images/external-link.png" width="12" height="12"/>
+            </svg>
+        </a>
         {% if site.algolia.enabled %}
         <span class="site-search">
           <input type="text" id="algolia-doc-search">