docs: add note for Auto Routing (Improved) changes

Author: kenjis

user_guide_src/source/changelogs/v4.2.0.rst

@@ -60,6 +60,8 @@ Behavior Changes
 Enhancements
 ************
 
+.. _v420-new-improved-auto-routing:
+
 New Improved Auto Routing
 =========================
 

user_guide_src/source/incoming/controllers.rst

@@ -153,6 +153,9 @@ Auto Routing (Improved)
 
 Since v4.2.0, the new more secure Auto Routing has been introduced.
 
+.. note:: If you are familiar with CodeIgniter 3's Auto Routing or Auto Routing (Legacy),
+    you can see the differences in :ref:`ChangeLog v4.2.0 <v420-new-improved-auto-routing>`.
+
 This section describes the functionality of the new auto-routing.
 It automatically routes an HTTP request, and executes the corresponding controller method
 without route definitions.

user_guide_src/source/incoming/routing.rst

@@ -585,6 +585,9 @@ Auto Routing (Improved)
 
 Since v4.2.0, the new more secure Auto Routing has been introduced.
 
+.. note:: If you are familiar with CodeIgniter 3's Auto Routing or Auto Routing (Legacy),
+    you can see the differences in :ref:`ChangeLog v4.2.0 <v420-new-improved-auto-routing>`.
+
 When no defined route is found that matches the URI, the system will attempt to match that URI against the controllers and methods when Auto Routing is enabled.
 
 .. important:: For security reasons, if a controller is used in the defined routes, Auto Routing (Improved) does not route to the controller.