Set content type of package desription

Author: p-snft

setup.py

@@ -19,6 +19,7 @@ def read(fname):
       author_email='[email protected]',
       description='Demandlib of the open energy modelling framework',
       long_description=read('README.rst'),
+      long_description_content_type='text/x-rst',
       packages=find_packages(),
       install_requires=['numpy >= 1.17.0',
                         'pandas >= 1.0'],