Added license file to setup

setup.cfg

@@ -1,2 +1,3 @@
 [metadata]
-description-file = README.md
+description-file = README.md
+license_files = LICENSE.txt

setup.py

@@ -30,6 +30,7 @@ def setup_package():
           url='https://gitlab.astro-wise.org/micado/atmosphericmodel',
           download_url='https://gitlab.astro-wise.org/micado/atmosphericmodel/-/archive/v_01/atmosphericmodel-v_01.tar.gz',
           license='GNU General Public License v3',
+          data_files = [('',['LICENSE.txt'])],
           package_dir={'AstroAtmosphere': 'AstroAtmosphere'},
           package_data={'AstroAtmosphere': ['data/*.txt']},
           include_package_data=True,