add comment block

src/kraken_headers.hpp

@@ -1,3 +1,22 @@
+/*
+ * Copyright 2013-2014, Derrick Wood <dwood@cs.umd.edu>
+ *
+ * This file is part of the Kraken taxonomic sequence classification system.
+ *
+ * Kraken 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.
+ *
+ * Kraken 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 Kraken.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
 #ifndef KRAKEN_HEADERS_HPP
 #define KRAKEN_HEADERS_HPP