move migration docs to new separate page, leave callout on getting started page; fixes #12244

docs/_includes/nav-getting-started.html

@@ -28,12 +28,6 @@
 </li>
 <li>
   <a href="#migration">Migrating from 2.x to 3.0</a>
-  <ul class="nav">
-    <li><a href="#migration-classes">Major class changes</a></li>
-    <li><a href="#migration-new">What's new</a></li>
-    <li><a href="#migration-dropped">What's removed</a></li>
-    <li><a href="#migration-notes">Additional notes</a></li>
-  </ul>
 </li>
 <li>
   <a href="#support">Browser and device support</a>

docs/_includes/nav-migration.html

+<li>
+  <a href="#classes">Major class changes</a>
+</li>
+<li>
+  <a href="#new">What's new</a>
+</li>
+<li>
+  <a href="#dropped">What's removed</a>
+</li>
+<li>
+  <a href="#notes">Additional notes</a>
+</li>

docs/_layouts/default.html

@@ -40,6 +40,8 @@
                 {% include nav-customize.html %}
               {% elsif page.slug == "about" %}
                 {% include nav-about.html %}
+              {% elsif page.slug == "migration" %}
+                {% include nav-migration.html %}
               {% endif %}
             </ul>
           </div>