Added a deprecated directive

Author: javiereguiluz

components/browser_kit.rst

@@ -37,11 +37,16 @@ Creating a Client
 ~~~~~~~~~~~~~~~~~
 
 The component only provides an abstract client and does not provide any backend
-ready to use for the HTTP layer.
+ready to use for the HTTP layer. To create your own client, you must extend the
+``AbstractBrowser`` class and implement the
+:method:`Symfony\\Component\\BrowserKit\\AbstractBrowser::doRequest` method.
 
-To create your own client, you must extend the ``AbstractBrowser`` class and
-implement the :method:`Symfony\\Component\\BrowserKit\\AbstractBrowser::doRequest` method.
-This method accepts a request and should return a response::
+.. deprecated:: 4.3
+
+    In Symfony 4.3 and earlier versions, the ``AbstractBrowser`` class was called
+    ``Client`` (which is now deprecated).
+
+The ``doRequest()`` method accepts a request and should return a response::
 
     namespace Acme;