Add missing versionadded directive. refs #11956

Author: OskarStark

components/dotenv.rst

@@ -151,11 +151,15 @@ Use environment variables in values by prefixing variables with ``$``:
 
 Define a default value in case the environment variable is not set:
 
- .. code-block:: terminal
+.. code-block:: terminal
 
     DB_USER=
     DB_PASS=${DB_USER:-root}pass # results in DB_PASS=rootpass
 
+.. versionadded:: 4.4
+
+    The support for default values has been introduced in Symfony 4.4.
+
 Embed commands via ``$()`` (not supported on Windows):
 
 .. code-block:: terminal