docs: add link to how-to page

Author: kenjis

user_guide_src/source/database/configuration.rst

@@ -105,6 +105,8 @@ within the class' constructor:
 
 .. literalinclude:: configuration/008.php
 
+.. _database-config-with-env-file:
+
 **************************
 Configuring with .env File
 **************************

user_guide_src/source/general/configuration.rst

@@ -237,6 +237,8 @@ expect your ``Config\App`` to magically have that property and value at run time
 When you have the property ``$default = ['encrypt' => false]`` in your
 ``Config\Database``, you cannot change the ``encrypt`` value to an array even if
 you put ``database.default.encrypt.ssl_verify = true`` in your **.env**.
+If you want to do like that, see
+:ref:`Database Configuration <database-config-with-env-file>`.
 
 Treating Environment Variables as Arrays
 ========================================