Add a warning about missing headers on the request

Author: joelwurtz

clients/socket-client.rst

@@ -63,4 +63,10 @@ use case would be::
     ];
     $client = new Client($messageFactory, $options);
 
+.. warning::
+
+    This client assume that the request is compliant with HTTP 2.0, 1.1 or 1.0 standard. So a request without a ``Host`` header, or 
+    with a body but wihout a ``Content-Length`` will certainly fail. You can make sure that requests used by this client are valid, by
+    decorating it with :doc:`plugins </plugins/introduction>` like ``ContentLengthPlugin`` or ``HeaderDefaultsPlugin``.
+
 .. include:: includes/further-reading-sync.inc