Change label to HTTP adapter configuration

Author: ddeboer

doc/includes/custom-headers.rst

@@ -1,3 +1,4 @@
 This allows you to pass headers that are different between purge requests.
 If you want to add a header to all purge requests, such as ``Authorization``,
-use a :ref:`custom HTTP client <custom HTTP client>` instead.
+:ref:`HTTP adapter configuration <configure the HTTP adapter>` to use a
+custom HTTP client instead.

doc/proxy-clients.rst

@@ -12,8 +12,8 @@ which caching solution you use.
 Setup
 -----
 
-Install HTTP Adapter
-~~~~~~~~~~~~~~~~~~~~
+HTTP Adapter Installation
+~~~~~~~~~~~~~~~~~~~~~~~~~
 
 Because the clients send invalidation requests over HTTP, an `HTTP adapter`_
 must be installed. Which one you need depends on the HTTP client library that
@@ -38,10 +38,10 @@ Alternatively:
 
     $ composer require zendframework/zend-diactoros
 
-.. _custom HTTP client:
+.. _HTTP adapter configuration:
 
-Pass an HTTP Adapter Explicitly
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+HTTP Adapter Configuration
+~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 By default, the proxy client will find the adapter that you have installed
 through Composer. But you can also pass the adapter explicitly. This is most