docs: broken link htmx ajax-header

Author: ddevsr

user_guide_src/source/general/ajax.rst

@@ -56,7 +56,7 @@ React
 htmx
 ====
 
-You can use `ajax-header <https://htmx.org/extensions/ajax-header/>`_ extension.
+You can use `ajax-header <https://github.com/bigskysoftware/htmx-extensions/blob/main/src/ajax-header/README.md>`_ extension.
 
 .. code-block:: html