docs: add upgrading and changelog

Author: kenjis

user_guide_src/source/changelogs/v4.1.5.rst

@@ -13,6 +13,7 @@ BREAKING
 ========
 
 - Fixed `a bug <https://github.com/codeigniter4/CodeIgniter4/issues/2913>`_ on CSRF protection. Now CSRF protection works on PUT/PATCH/DELETE requests when CSRF filter is applied. If you use such requests, you need to send CSRF token.
+- In the previous version, ``CURLRequest`` sends request headers from the browser, because of a bug. Since this version it does not send them.
 
 Enhancements
 ============

user_guide_src/source/installation/upgrade_415.rst

@@ -53,6 +53,14 @@ If you want the same behavior as the previous version, set the CSRF filter like
 
 Protecting **GET** method needs only when you use ``form_open()`` auto-generation of CSRF field.
 
+CURLRequest header change
+-------------------------
+
+Because of a bug, the previous version of ``CURLRequest`` sends the request headers from the browser request.
+The bug was fixed. If your requests depend on the headers, your requests might fail after upgrading.
+In this case, add the necessary headers manually.
+See `CURLRequest Class <../libraries/curlrequest.html#headers>`_ for how to add.
+
 Breaking Enhancements
 =====================