docs: declare GPL3 license

refs #2672

Change-Id: I93e0cb6b7ff907d3f05d21aae2d21009efd3e2f0
diff --git a/tools/peek/version.hpp b/tools/peek/version.hpp
index 4baf76e..9c758ba 100644
--- a/tools/peek/version.hpp
+++ b/tools/peek/version.hpp
@@ -1,5 +1,28 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /**
+ * Copyright (c) 2014-2015,  Regents of the University of California,
+ *                           Arizona Board of Regents,
+ *                           Colorado State University,
+ *                           University Pierre & Marie Curie, Sorbonne University,
+ *                           Washington University in St. Louis,
+ *                           Beijing Institute of Technology,
+ *                           The University of Memphis.
+ *
+ * This file is part of ndn-tools (Named Data Networking Essential Tools).
+ * See AUTHORS.md for complete list of ndn-tools authors and contributors.
+ *
+ * ndn-tools 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.
+ *
+ * ndn-tools 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
+ * ndn-tools, e.g., in COPYING.md file.  If not, see <http://www.gnu.org/licenses/>.
+ */
+/**
  * Copyright (c) 2014,  Regents of the University of California,
  *                      Arizona Board of Regents,
  *                      Colorado State University,