[copyright] Add missing copyright headers

contrib/seeds/makeseeds.py

@@ -1,4 +1,7 @@
 #!/usr/bin/env python
+# Copyright (c) 2013-2015 The Bitcoin Core developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or http://www.opensource.org/licenses/mit-license.php.
 #
 # Generate seeds.txt from Pieter's DNS seeder
 #