docs: add an example to the header changes

Author: michalsn

user_guide_src/source/changelogs/v4.6.0.rst

@@ -109,6 +109,38 @@ In previous versions, headers set by the ``Response`` class were added to existi
 ones - giving no options to change them. That could lead to unexpected behavior when
 the same headers were set with mutually exclusive directives.
 
+For example, session will automatically set headers with the ``header()`` function:
+
+.. code-block:: none
+
+    Expires: Thu, 19 Nov 1981 08:52:00 GMT
+    Cache-Control: no-store, no-cache, must-revalidate
+    Pragma: no-cache
+
+So if we set **Expires** header one more time we will end up with a duplicated header:
+
+.. code-block:: php
+
+    $response->removeHeader('Expires'); // has no effect
+    return $response->setHeader('Expires', 'Sun, 17 Nov 2024 14:17:37 GMT');
+
+Response headers:
+
+.. code-block:: none
+
+    Expires: Thu, 19 Nov 1981 08:52:00 GMT
+    // ...
+    Expires: Sun, 17 Nov 2024 14:17:37 GMT
+
+Now, we don't know which one will be picked by the browser or which header is the correct one.
+With changes in this version our previous header will be override:
+
+.. code-block:: none
+
+    Cache-Control: no-store, no-cache, must-revalidate
+    Pragma: no-cache
+    Expires: Sun, 17 Nov 2024 14:17:37 GMT
+
 Interface Changes
 =================