add license header

Author: abbbi

nullfs.c

@@ -1,9 +1,23 @@
 /*
  * Nullfs.
  *
- * Copyright 2018 Michael Ablassmeier <[email protected]>
- * 
- * This file may be redistributed under the terms of the GNU GPL.
+ *
+ *   Copyright (C) 2018  Michael Ablassmeier <[email protected]>
+ *
+ *   This program is free software: you can redistribute it and/or modify
+ *   it under the terms of the GNU General Public License as published by
+ *   the Free Software Foundation, either version 3 of the License, or
+ *   (at your option) any later version.
+ *
+ *   This program is distributed in the hope that it will be useful,
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *   GNU General Public License for more details.
+ *
+ *   You should have received a copy of the GNU General Public License
+ *   along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ *
  *
  * Create a file system that stores its structure in memory but
  * written data is sent to a blackhole. May be used for performance