Adding AUTHORS and changing copyright headers to refer to it.

Change-Id: I17fc6fa86a4a98ed6e4c8df0ff9333ae04b337c7
diff --git a/main.c b/main.c
index 0c2dcba..37b79ee 100644
--- a/main.c
+++ b/main.c
@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0-only
 /*
- * Copyright 2018 Google LLC
+ * Copyright 2018 The Hafnium Authors.
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License