Adding license headers.

Signed-off-by: Pol Henarejos <pol.henarejos@cttc.es>

CMakeLists.txt

@@ -1,3 +1,20 @@
+ # 
+ # This file is part of the Pico HSM distribution (https://github.com/polhenarejos/pico-hsm).
+ # Copyright (c) 2022 Pol Henarejos.
+ # 
+ # This program is free software: you can redistribute it and/or modify  
+ # it under the terms of the GNU General Public License as published by  
+ # the Free Software Foundation, version 3.
+ #
+ # This program is distributed in the hope that it will be useful, but 
+ # WITHOUT ANY WARRANTY; without even the implied warranty of 
+ # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 
+ # General Public License for more details.
+ #
+ # You should have received a copy of the GNU General Public License 
+ # along with this program. If not, see <http://www.gnu.org/licenses/>.
+ #
+
 cmake_minimum_required(VERSION 3.13)
 
 include(pico_sdk_import.cmake)