STM32_gen_PeripheralPins.py : Add license header

Author: jeromecoutant

tools/targets/STM32_gen_PeripheralPins.py

@@ -1,3 +1,20 @@
+"""
+* mbed Microcontroller Library
+* Copyright (c) 2006-2018 ARM Limited
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+*     http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+"""
+
 import argparse
 import datetime
 import fnmatch