docs: add sub section titles

Author: kenjis

user_guide_src/source/outgoing/response.rst

@@ -43,6 +43,9 @@ You can set format an array into either JSON or XML and set the content type hea
 Setting Headers
 ---------------
 
+setHeader()
+^^^^^^^^^^^
+
 Often, you will need to set headers to be set for the response. The Response class makes this very simple to do,
 with the ``setHeader()`` method.
 
@@ -54,12 +57,18 @@ which can be either a string or an array of values that will be combined correct
 Using these functions instead of using the native PHP functions allows you to ensure that no headers are sent
 prematurely, causing errors, and makes testing possible.
 
+appendHeader()
+^^^^^^^^^^^^^^
+
 If the header exists and can have more than one value, you may use the ``appendHeader()`` and ``prependHeader()``
 methods to add the value to the end or beginning of the values list, respectively. The first parameter is the name
 of the header, while the second is the value to append or prepend.
 
 .. literalinclude:: response/005.php
 
+removeHeader()
+^^^^^^^^^^^^^^
+
 Headers can be removed from the response with the ``removeHeader()`` method, which takes the header name as the only
 parameter. This is not case-sensitive.