help with php-http adapter in changelog and setup instructions

Author: dbu

CHANGELOG.md

@@ -6,7 +6,9 @@ See also the [GitHub releases page](https://github.com/FriendsOfSymfony/FOSHttpC
 2.0.0 (unreleased)
 ------------------
 
-* Replace hard coupling on Guzzle HTTP client with HTTP adapter.
+* Replace hard coupling on Guzzle HTTP client with HTTP adapter. You now need
+  to explicitly specify the adapter you want, see [installation instructions]
+  (http://foshttpcache.readthedocs.org/en/stable/installation.html)
 * The NGINX purge location is no longer passed as constructor argument but by
   calling `setPurgeLocation()`.
 * In ProxyTestCase, `getHttpClient()` has been replaced with `getHttpAdapter()`;

doc/installation.rst

@@ -9,11 +9,23 @@ Composer_:
 
 .. code-block:: bash
 
-    $ composer require friendsofsymfony/http-cache:~1.0
+    $ composer require friendsofsymfony/http-cache:~2.0
+
+Note that the library needs a ``psr/http-message-implementation`` and
+``php-http/adapter-implementation``. If your project does not contain one,
+composer will complain that it did not find ``psr/http-message-implementation``.
+
+When on PHP 5.5+, use the following line instead:
+
+.. code-block:: bash
+
+    $ composer require friendsofsymfony/http-cache:~2.0 guzzlehttp/psr7:^1.0 php-http/guzzle6-adapter:^0.1.0
+
+On PHP 5.4, the ``php-http/guzzle5-adapter:^0.1.0`` works fine.
 
 .. note::
 
-    This library follows `Semantic Versioning`_. Because constraint ``~1.0``
+    This library follows `Semantic Versioning`_. Because constraint ``~2.0``
     will only increment the minor and patch numbers, it will not introduce BC
     breaks.