minor #8758 adding more details about sessions, including how to activate (weaverryan)

This PR was squashed before being merged into the 4.0 branch (closes #8758).

Discussion
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adding more details about sessions, including how to activate

Just some things I thought of, after merging to session overhaul for 4.0.

Commits
-------

b95f550 yaml
29cd499 removing diff - does not work with config block
349f3e3 adding more details about sessions, including how to activate

Author: weaverryan

controller.rst

@@ -417,10 +417,6 @@ front controller - see :ref:`page-creation-environments`).
 You'll want to customize the error page your user sees. To do that, see
 the :doc:`/controller/error_pages` article.
 
-.. index::
-   single: Controller; The session
-   single: Session
-
 .. _controller-request-argument:
 
 The Request object as a Controller Argument
@@ -443,13 +439,61 @@ object. To get it in your controller, just add it as an argument and
 :ref:`Keep reading <request-object-info>` for more information about using the
 Request object.
 
+.. index::
+   single: Controller; The session
+   single: Session
+
+.. _session-intro:
+
 Managing the Session
 --------------------
 
 Symfony provides a nice session object that you can use to store information
 about the user between requests. By default, Symfony stores the token in a
 cookie and writes the attributes to a file by using native PHP sessions.
 
+First, enable sessions in your configuration:
+
+.. configuration-block::
+
+    .. code-block:: yaml
+
+        # config/packages/framework.yaml
+        framework:
+            # ...
+
+            session:
+                # With this config, PHP's native session handling is used
+                handler_id: ~
+
+    .. code-block:: xml
+
+        <!-- config/packages/framework.xml -->
+        <?xml version="1.0" encoding="UTF-8" ?>
+        <container xmlns="http://symfony.com/schema/dic/services"
+            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+            xmlns:framework="http://symfony.com/schema/dic/symfony"
+            xsi:schemaLocation="http://symfony.com/schema/dic/services
+                http://symfony.com/schema/dic/services/services-1.0.xsd
+                http://symfony.com/schema/dic/symfony
+                http://symfony.com/schema/dic/symfony/symfony-1.0.xsd">
+
+            <framework:config>
+                <!-- ... -->
+                <framework:session handler-id="null" />
+            </framework:config>
+        </container>
+
+    .. code-block:: php
+
+        // config/packages/framework.php
+        $container->loadFromExtension('framework', array(
+            'session' => array(
+                // ...
+                'handler_id' => null,
+            ),
+        ));
+
 To retrieve the session, add the :class:`Symfony\\Component\\HttpFoundation\\Session\\SessionInterface`
 type-hint to your argument and Symfony will provide you with a session::
 
@@ -474,6 +518,8 @@ Stored attributes remain in the session for the remainder of that user's session
     Every ``SessionInterface`` implementation is supported. If you have your
     own implementation, type-hint this in the arguments instead.
 
+For more info, see :doc:`/session`.
+
 .. index::
    single: Session; Flash messages
 

session.rst

@@ -1,6 +1,14 @@
 Sessions
 ========
 
+Symfony provides a nice session object that you can use to store information
+about the user between requests.
+
+To see how to use the session, read :ref:`session-intro`.
+
+More about Sessions
+-------------------
+
 .. toctree::
     :maxdepth: 1
 
@@ -10,3 +18,4 @@ Sessions
     session/php_bridge
     session/proxy_examples
 
+* :doc:`/doctrine/pdo_session_storage`