Include H3 in docs TOC

Author: muhammad-ali-pk

templates/docs/document.html

@@ -118,7 +118,14 @@ <h4 class="p-table-of-contents__header">On this page</h4>
             <nav class="p-table-of-contents__nav" aria-label="Table of contents">
               <ul class="p-table-of-contents__list">
                 {% for heading in document.headings_map %}
-                <li class="p-table-of-contents__item"><a class="p-table-of-contents__link" href="#{{ heading.heading_slug }}">{{ heading.heading_text }}</a></li>
+                  <li class="p-table-of-contents__item"><a class="p-table-of-contents__link" href="#{{ heading.heading_slug }}">{{ heading.heading_text }}</a></li>
+                    {% if heading.children %}
+                      <ul class="p-table-of-contents__list">
+                        {% for child in heading.children %}
+                          <li class="p-table-of-contents__item"><a class="p-table-of-contents__link" href="#{{ child.heading_slug }}">{{ child.heading_text }}</a></li>
+                        {% endfor %}
+                      </ul>
+                    {% endif %}
                 {% endfor %}
               </ul>
             </nav>