Used autoloaded AppKernel

Composer is perfectly capable of autoloading AppKernel (via the `classmap` autoloader),
this is the approach used in the [Symfony Standard Edition](https://github.com/symfony/symfony-standard/blob/05bca699ef631d03d4b114b4366ad0c180b55ecb/composer.json#L8).

Author: gnugat

Bootstraps/Symfony.php

@@ -27,10 +27,6 @@ public function __construct($appenv)
      */
     public function getApplication()
     {
-        if (file_exists('./app/AppKernel.php')) {
-            require_once './app/AppKernel.php';
-        }
-
         $this->includeAutoload();
 
         $app = new \AppKernel($this->appenv, false);

README.md

@@ -12,3 +12,12 @@ HttpKernel adapter for use of Symfony and Laravel frameworks with PHP-PM. See ht
 
         composer require php-pm/httpkernel-adapter:dev-master
 
+> **Note**: Make sure your `AppKernel` is autoloaded in your `composer.json`:
+>
+> ```
+> {
+>     "autoload": {
+>         "classmap": ["app/AppKernel.php"]
+>     }
+> }
+> ```