LibC: Claim some copyright for stdio

I've written a large part of the new stdio, so I'm (partly) to blame for it now.

Libraries/LibC/stdio.cpp

@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2020, Sergey Bugaev <bugaevc@serenityos.org>
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without