Update README.markdown

Fix example how to use `CachedHttpClient`. Fix #27

Author: stloyd

README.markdown

@@ -66,7 +66,16 @@ From `$client` object, you can access to all GitHub.
 // This file is generated by Composer
 require_once 'vendor/autoload.php';
 
-$client = new Github\Client(new CachedHttpClient(new FilesystemCache('/tmp/github-api-cache')));
+$client = new Github\Client(
+    new Github\HttpClient\CachedHttpClient(array('cache_dir' => '/tmp/github-api-cache')
+);
+
+// Or select directly which cache you want to use
+$client = new Github\Client(
+    new Github\HttpClient\CachedHttpClient(
+        new Github\HttpClient\Cache\FilesystemCache('/tmp/github-api-cache')
+    )
+);
 ```
 
 Using cache, the client will get cached responses if resources haven't changed since last time,