docs: add sub section titles

Author: kenjis

user_guide_src/source/incoming/routing.rst

@@ -269,19 +269,28 @@ extensive set of routes that all share the opening string, like when building an
 
 This would prefix the **users** and **blog** URIs with **admin**, handling URLs like **admin/users** and **admin/blog**.
 
+Setting Namespace
+-----------------
+
 If you need to assign options to a group, like a :ref:`assigning-namespace`, do it before the callback:
 
 .. literalinclude:: routing/024.php
 
 This would handle a resource route to the ``App\API\v1\Users`` controller with the **api/users** URI.
 
+Setting Filters
+---------------
+
 You can also use a specific :doc:`filter <filters>` for a group of routes. This will always
 run the filter before or after the controller. This is especially handy during authentication or api logging:
 
 .. literalinclude:: routing/025.php
 
 The value for the filter must match one of the aliases defined within **app/Config/Filters.php**.
 
+Nesting Groups
+--------------
+
 It is possible to nest groups within groups for finer organization if you need it:
 
 .. literalinclude:: routing/026.php
@@ -290,6 +299,9 @@ This would handle the URL at **admin/users/list**.
 
 .. note:: Options passed to the outer ``group()`` (for example ``namespace`` and ``filter``) are not merged with the inner ``group()`` options.
 
+Setting Other Options
+---------------------
+
 At some point, you may want to group routes for the purpose of applying filters or other route
 config options like namespace, subdomain, etc. Without necessarily needing to add a prefix to the group, you can pass
 an empty string in place of the prefix and the routes in the group will be routed as though the group never existed but with the