Adds a Video Courses link to the Learn drop down (vuejs#2099)

* Adds a Video Courses link to the drop down

* Moved to bottom of learn list

* Adding subsection for Learn dropdown

* Now with proper indentation

Author: Gregg

themes/vue/layout/partials/learn_dropdown.ejs

@@ -1,12 +1,21 @@
 <li class="nav-dropdown-container learn">
   <a class="nav-link<%- page.path.match(/\/(guide(?!\/team.html$)|api|style-guide|examples|cookbook)(\/|$)/) ? ' current' : '' %>">Learn</a><span class="arrow"></span>
   <ul class="nav-dropdown">
-    <li><ul>
-      <li><a href="<%- url_for("/v2/guide/") %>" class="nav-link<%- page.path.match(/\/guide(\/|$)/) ? ' current' : '' %>">Guide</a></li>
-      <li><a href="<%- url_for("/v2/api/") %>" class="nav-link<%- page.path.match(/\/api(\/|$)/) ? ' current' : '' %>">API</a></li>
-      <li><a href="<%- url_for("/v2/style-guide/") %>" class="nav-link<%- page.path.match(/\/style-guide(\/|$)/) ? ' current' : '' %>">Style Guide</a></li>
-      <li><a href="<%- url_for("/v2/examples/") %>" class="nav-link<%- page.path.match(/\/examples(\/|$)/) ? ' current' : '' %>">Examples</a></li>
-      <li><a href="<%- url_for("/v2/cookbook/") %>" class="nav-link<%- page.path.match(/\/cookbook(\/|$)/) ? ' current' : '' %>">Cookbook</a></li>
-    </ul></li>
+    <li><h4>Documentation</h4></li>
+    <li>
+      <ul>
+        <li><a href="<%- url_for("/v2/guide/") %>" class="nav-link<%- page.path.match(/\/guide(\/|$)/) ? ' current' : '' %>">Guide</a></li>
+        <li><a href="<%- url_for("/v2/api/") %>" class="nav-link<%- page.path.match(/\/api(\/|$)/) ? ' current' : '' %>">API</a></li>
+        <li><a href="<%- url_for("/v2/style-guide/") %>" class="nav-link<%- page.path.match(/\/style-guide(\/|$)/) ? ' current' : '' %>">Style Guide</a></li>
+        <li><a href="<%- url_for("/v2/examples/") %>" class="nav-link<%- page.path.match(/\/examples(\/|$)/) ? ' current' : '' %>">Examples</a></li>
+        <li><a href="<%- url_for("/v2/cookbook/") %>" class="nav-link<%- page.path.match(/\/cookbook(\/|$)/) ? ' current' : '' %>">Cookbook</a></li>
+      </ul>
+    </li>
+    <li><h4>Video Courses</h4></li>
+    <li>
+      <ul>
+        <li><a href="https://www.vuemastery.com/courses/" class="nav-link" target="_blank">Vue Mastery</a></li>
+      </ul>
+    </li>
   </ul>
 </li>