Docs: enable show_related

This turns on the topic hierarchy and the previous/next navigation
links.

Change-Id: If64a813afd662d741e478e1760868a6da3493cbd

doc/source/conf.py

@@ -96,7 +96,9 @@ pygments_style = 'sphinx'
 # Theme options are theme-specific and customize the look and feel of a theme
 # further.  For a list of options available for each theme, see the
 # documentation.
-#html_theme_options = {}
+html_theme_options = {
+    'show_related': True
+}
 
 # Add any paths that contain custom themes here, relative to this directory.
 #html_theme_path = []