[symfony#2856] Indenting paragraph and fixing a few minor things

cookbook/session/php_bridge.rst

@@ -35,12 +35,13 @@ the example below:
 
 .. note::
 
-If the legacy application requires it's own session save-handler, do not
-override this, rather set ``handler_id: ~``. Note that a save handler cannot
-be changed once the session has been started. If the application starts the
-session before Symfony initializes the save-handler will have already been 
-set. You will need ``handler_id: ~``. Only override the save-handler if you
-are sure the legacy application can use the Symfony save-handler without
-side effects and that the session has not been started before Symfony inializes.
+    If the legacy application requires its own session save-handler, do not
+    override this. Instead set ``handler_id: ~``. Note that a save handler
+    cannot be changed once the session has been started. If the application
+    starts the session before Symfony is initialized, the save-handler will
+    have already been  set. In this case, you will need ``handler_id: ~``.
+    Only override the save-handler if you are sure the legacy application
+    can use the Symfony save-handler without side effects and that the session
+    has not been started before Symfony is initialized.
 
 For more details, see :doc:`/components/http_foundation/session_php_bridge`.