docs: add general instruction and section title

Author: kenjis

user_guide_src/source/installation/upgrade_423.rst

@@ -2,8 +2,17 @@
 Upgrading from 4.2.2 to 4.2.3
 #############################
 
+Please refer to the upgrade instructions corresponding to your installation method.
+
+- :ref:`Composer Installation App Starter Upgrading <app-starter-upgrading>`
+- :ref:`Composer Installation Adding CodeIgniter4 to an Existing Project Upgrading <adding-codeigniter4-upgrading>`
+- :ref:`Manual Installation Upgrading <installing-manual-upgrading>`
+
 .. contents::
     :local:
     :depth: 2
 
+Project Files
+*************
+
 Version ``4.2.3`` is an internal change for security measures and requires no intervention in projects.