Document conditional TOC rendering (#1376)

* Document conditional TOC rendering

* Simplify demonstration of conditional rendering

docs/content/documentation/content/table-of-contents.md

@@ -12,8 +12,9 @@ documentation for information on its structure.
 Here is an example of using that field to render a two-level table of contents:
 
 ```jinja2
-<ul>
-{% for h1 in page.toc %}
+{% if page.toc %}
+    <ul>
+    {% for h1 in page.toc %}
         <li>
             <a href="{{h1.permalink | safe}}">{{ h1.title }}</a>
             {% if h1.children %}
@@ -26,8 +27,9 @@ Here is an example of using that field to render a two-level table of contents:
                 </ul>
             {% endif %}
         </li>
-{% endfor %}
-</ul>
+    {% endfor %}
+    </ul>
+{% endif %}
 ```
 
 While headers are neatly ordered in this example, it will work just as well with disjoint headers.