adds license information

counters_option.py

 #! /usr/bin/python3
 
+# SPDX-License-Identifier: GPL-3.0-or-later
+# Copyright (C) 2018-2021 Georges Da Costa <georges.da-costa@irit.fr>
+
 linux_include = '/usr/include/linux/perf_event.h'
 
 string = """#include <linux/perf_event.h>