minor #18832 Document session cookie in response (alamirault)

This PR was merged into the 5.4 branch.

Discussion
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Document session cookie in response

Try to document #15777

I'm not convinced by my wording, but let's do better together !

Commits
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c1f88e6 Document session cookie in response

Author: javiereguiluz

session.rst

@@ -403,6 +403,13 @@ Check out the Symfony config reference to learn more about the other available
     ``session.auto_start = 1`` This directive should be turned off in
     ``php.ini``, in the web server directives or in ``.htaccess``.
 
+Session cookie is available in the ``Response`` object. It's useful in the CLI context
+or php runtime with runners like Roadrunner or Swoole.
+
+.. versionadded:: 5.4
+
+    Accessing to the session cookie in the ``Response`` object was introduced in Symfony 5.4.
+
 Session Idle Time/Keep Alive
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~