improve .env doc

Author: houssemzi

configuration.rst

@@ -583,6 +583,12 @@ 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).
 
+.. tip::
+
+    Since the ``.env`` file is read and parsed on every request, you don't need to
+clear the cache on ``dev`` environment nor to restart the (PHP) container in case
+you are using docker.
+
 .env File Syntax
 ................