Update configuration.rst for dotenv command

It explains how can they register dotenv command and run it properly

Author: mertingen

configuration.rst

@@ -773,7 +773,24 @@ the easiest way to define env vars is by deploying a ``.env.local`` file to your
 production server(s) with your production values.
 
 To improve performance, you can optionally run the ``dotenv:dump`` command (available
-in :ref:`Symfony Flex <symfony-flex>` 1.2 or later):
+in :ref:`Symfony Flex <symfony-flex>` 1.2 or later). The command is not registered by default. 
+In order to enable it, you must add it to their services.yaml file:
+
+.. code-block:: yaml
+
+    services:
+        Symfony\Component\Dotenv\Command\DotenvDumpCommand:
+            - '%kernel.project_dir%/.env'
+            - '%kernel.environment%'
+
+On PHP >= 8, the two arguments can be removed when autoconfiguration is enabled (which is the default):
+
+.. code-block:: yaml
+
+    services:
+        Symfony\Component\Dotenv\Command\DotenvDumpCommand: ~
+        
+Running command:
 
 .. code-block:: terminal