update file headers with license information (SPDX)
diff --git a/examples/port_publisher.py b/examples/port_publisher.py
index 8786733..a87be65 100755
--- a/examples/port_publisher.py
+++ b/examples/port_publisher.py
@@ -1,4 +1,8 @@
 #! /usr/bin/env python

+#

+# (C) 2001-2015 Chris Liechti <cliechti@gmx.net>

+#

+# SPDX-License-Identifier:    BSD-3-Clause

 """\

 Multi-port serial<->TCP/IP forwarder.

 - RFC 2217