Add licensing and copyright information in readme and source code

[NicolasToussaint]

While the MIT licence is mentioned in the Readme file, the licence text itself copyright information are missing.

We could add a LICENSE.md file with the MI licence text, and include licensing + copyright info as proposed in the REUSE.Software standard in each source code file:

/*
 * SPDX-FileCopyrightText: 2024 Jane Doe <jane@example.com>
 *
 * SPDX-License-Identifier: MIT
 */