Create a README file for the inclusion case

# Folder instructions

This directory contains test data for models made up by a sphere with inclusions.

# License

   Copyright (C) 2024   INAF - Osservatorio Astronomico di Cagliari

   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, either version 3 of the License, or

   (at your option) any later version.

   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.

   A copy of the GNU General Public License is distributed along with

   this program in the COPYING file. If not, see: <https://www.gnu.org/licenses/>.