[Configuration] Add $_ENV and $_SERVER example with .env

Author: alexandre-daubois

configuration.rst

@@ -58,7 +58,7 @@ Configuration Formats
 ~~~~~~~~~~~~~~~~~~~~~
 
 Unlike other frameworks, Symfony doesn't impose a specific format on you to
-configure your applications, but lets you choose between YAML, XML and PHP. 
+configure your applications, but lets you choose between YAML, XML and PHP.
 Throughout the Symfony documentation, all configuration examples will be
 shown in these three formats.
 
@@ -721,6 +721,12 @@ This file should be committed to your repository and (due to that fact) should
 only contain "default" values that are good for local development. This file
 should not contain production values.
 
+Your env vars can be accessed in your code thanks to PHP super
+globals ``$_ENV`` and ``$_SERVER``. Both are equivalent::
+
+    $databaseUrl = $_ENV['DATABASE_URL']; // mysql://db_user:db_password@127.0.0.1:3306/db_name
+    $env = $_SERVER['APP_ENV']; // prod
+
 In addition to your own env vars, this ``.env`` file also contains the env vars
 defined by the third-party packages installed in your application (they are
 added automatically by :ref:`Symfony Flex <symfony-flex>` when installing packages).