Add license statement to README files

The current implementation offers a set of elementary tests to check that the original FORTRAN code can be compiled and executed on a limited set of pre-defined input data. The functionality of this initial stage can be verified by cloning the gitLab repository on a local machine and building the binaries from the `src` folder.

*NOTE:* The building process requires a working installation of the GNU Compiler Collection (`gcc`), of the GNU FORTRAN compiler (`gfortran`) and of the GNU `make` builder.

# License

This project is distributed under the terms of the *GNU General Public License V3.0 or later* (GPL-3.0-or-later). Check the contents of the *COPYING* file for further details.

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Distributed under the terms of *GNU GPL-3.0-or-later*

# Folder instructions

This directory collects all the output of make builds.

Distributed under the terms of *GNU GPL-3.0-or-later*

# Docker support for the NP-TMcode project

This Dockerfile allows to create mainly:

Distributed under the terms of *GNU GPL-3.0-or-later*

# Singularity support for the NP-TMcode project

This `np-tmcode-run.def` file allows to create a np-tmcode-run image, that contains only the pre-built executables, python test scripts, compiled documentation, and the minimal runtime to run them

Distributed under the terms of *GNU GPL-3.0-or-later*

# Folder instructions

This directory contains the material to build the project documentation with *doxygen*.