dist/tools/externc: add license

dist/tools/externc/check.sh

@@ -1,5 +1,12 @@
 #!/bin/sh
 
+# Copyright 2014 Ludwig Ortmann <ludwig.ortmann@fu-berlin.de>
+# Copyright 2014 DangNhat Pham-Huu <51002279@hcmut.edu.vn>
+#
+# This file is subject to the terms and conditions of the GNU Lesser
+# General Public License v2.1. See the file LICENSE in the top level
+# directory for more details.
+
 # customizable
 CHECKROOT=$(dirname "${0}")