[10.x] Document session except and only methods (#9230)

* document session except and only methods

* Update session.md

---------

Co-authored-by: Taylor Otwell <taylor@laravel.com>

Author: xurshudyan

session.md

@@ -144,6 +144,15 @@ If you would like to retrieve all the data in the session, you may use the `all`
 
     $data = $request->session()->all();
 
+<a name="retrieving-a-portion-of-the-session-data"></a>
+#### Retrieving a Portion of the Session Data
+
+The `only` and `except` methods may be used to retrieve a subset of the session data:
+
+    $data = $request->session()->only(['username', 'email']);
+
+    $data = $request->session()->except(['username', 'email']);
+
 <a name="determining-if-an-item-exists-in-the-session"></a>
 #### Determining if an Item Exists in the Session