Added missing \ prefix for the github classes to deal with namespaces

Author: fh

README.markdown

@@ -52,7 +52,7 @@ Now we can use autoloader from Composer by:
 // This file is generated by Composer
 require_once 'vendor/autoload.php';
 
-$client = new Github\Client();
+$client = new \Github\Client();
 $repositories = $client->api('user')->repositories('ornicar');
 ```
 
@@ -66,19 +66,19 @@ From `$client` object, you can access to all GitHub.
 // This file is generated by Composer
 require_once 'vendor/autoload.php';
 
-$client = new Github\Client(
-    new Github\HttpClient\CachedHttpClient(array('cache_dir' => '/tmp/github-api-cache'))
+$client = new \Github\Client(
+    new \Github\HttpClient\CachedHttpClient(array('cache_dir' => '/tmp/github-api-cache'))
 );
 
 // Or select directly which cache you want to use
-$client = new Github\HttpClient\CachedHttpClient();
+$client = new \Github\HttpClient\CachedHttpClient();
 $client->setCache(
     // Built in one, or any cache implementing this interface:
     // Github\HttpClient\Cache\CacheInterface
-    new Github\HttpClient\Cache\FilesystemCache('/tmp/github-api-cache')
+    new \Github\HttpClient\Cache\FilesystemCache('/tmp/github-api-cache')
 );
 
-$client = new Github\Client($client);
+$client = new \Github\Client($client);
 ```
 
 Using cache, the client will get cached responses if resources haven't changed since last time,