[Process] Make Process::start method chainable

src/Symfony/Component/Process/Process.php

@@ -224,6 +224,8 @@ class Process
      *
      * @param callback|null $callback A PHP callback to run whenever there is some
      *                                output available on STDOUT or STDERR
+     * 
+     * @return Process The process itself
      *
      * @throws RuntimeException When process can't be launch or is stopped
      * @throws RuntimeException When process is already running
@@ -329,6 +331,8 @@ class Process
         }
 
         $this->updateStatus();
+        
+        return $this;
     }
 
     /**