Add sidebar links between devel and sysadm instances.

---

Migrated from D6976 (view on Phabricator)

docs/_templates/layout.html

@@ -16,6 +16,27 @@
 <!-- End Matomo Code -->
 {% endblock %}
 
+
+{# copied from sphinx_rtd_theme/layout.html, with the extra System Administration link #}
+{%- block menu %}
+  {%- set toctree = toctree(maxdepth=theme_navigation_depth|int,
+                            collapse=theme_collapse_navigation|tobool,
+                            includehidden=theme_includehidden|tobool,
+                            titles_only=theme_titles_only|tobool) %}
+  {%- if toctree %}
+    {{ toctree }}
+  {%- else %}
+    <!-- Local TOC -->
+    <div class="local-toc">{{ toc }}</div>
+  {%- endif %}
+
+  <hr />
+
+  <ul>
+      <li class="toctree-l1"><a href="../sysadm/">System Administration</a></li>
+  </ul>
+{%- endblock %}
+
 {% block content %}
   <div class="swh-top-bar">
     <ul>