docs: add about controllers namespace in routing

Author: kenjis

user_guide_src/source/incoming/routing.rst

@@ -47,6 +47,23 @@ You can supply multiple verbs that a route should match by passing them in as an
 
 .. literalinclude:: routing/004.php
 
+Controller's Namespace
+======================
+
+If a controller name is stated without beginning with ``\``, the :ref:`routing-default-namespace` will be prepended:
+
+.. literalinclude:: routing/063.php
+
+If you put ``\`` at the beginning, it is treated as a fully qualified class name:
+
+.. literalinclude:: routing/064.php
+
+You can also specify the namespace with the ``namespace`` option:
+
+.. literalinclude:: routing/038.php
+
+See :ref:`assigning-namespace` for details.
+
 Placeholders
 ============
 
@@ -394,7 +411,7 @@ You specify an array for the filter value:
 Assigning Namespace
 -------------------
 
-While a default namespace will be prepended to the generated controllers (see below), you can also specify
+While a :ref:`routing-default-namespace` will be prepended to the generated controllers, you can also specify
 a different namespace to be used in any options array, with the ``namespace`` option. The value should be the
 namespace you want modified:
 
@@ -480,6 +497,8 @@ Routes Configuration Options
 The RoutesCollection class provides several options that affect all routes, and can be modified to meet your
 application's needs. These options are available at the top of **app/Config/Routes.php**.
 
+.. _routing-default-namespace:
+
 Default Namespace
 =================
 

user_guide_src/source/incoming/routing/063.php

@@ -0,0 +1,4 @@
+<?php
+
+// Routes to \App\Controllers\Users::index()
+$routes->get('users', 'Users::index');

user_guide_src/source/incoming/routing/064.php

@@ -0,0 +1,4 @@
+<?php
+
+// Routes to \Acme\Blog\Controllers\Home::list()
+$routes->get('blog', '\Acme\Blog\Controllers\Home::list');