update installation instructions

Author: xabbuh

README.md

@@ -14,21 +14,10 @@ Installation
 The recommended way to install the xAPI client is using
 [Composer](http://getcomposer.org/):
 
-1. Download and install Composer:
-
-        curl -sS http://getcomposer.org/installer | php
-
-   For more details on how to install composer have a look at the official
-   [documentation](http://getcomposer.org/doc/00-intro.md).
-
-1. Add ``xabbuh/xapi-client``, ``xabbuh/xapi-common``, ``xabbuh/xapi-model`` and
-   ``xabbuh/xapi-serializer`` as dependencies to your project:
+1. Add ``xabbuh/xapi-client`` as a dependency to your project:
 
     ```bash
-    $ composer require --no-update xabbuh/xapi-client "~1.0@dev"
-    $ composer require --no-update xabbuh/xapi-common "~1.0@dev"
-    $ composer require --no-update xabbuh/xapi-model "~1.0@dev"
-    $ composer require xabbuh/xapi-serializer "~1.0@dev"
+    $ composer require xabbuh/xapi-client
     ```
 
 1. Require Composer's autoloader: