Use distutils for sdist, not setuptools (#123)

Co-authored-by: Nikita Titov <[email protected]>

Author: vene

MANIFEST.in

@@ -1,4 +1,5 @@
 include MANIFEST.in
+include README.rst
 include Makefile
 include requirements*.txt
 recursive-include lightning *.c *.h *.cpp *.pyx *.pxd

setup.py

@@ -5,6 +5,7 @@
 import re
 import sys
 import os
+from distutils.command.sdist import sdist
 import setuptools
 from numpy.distutils.core import setup
 
@@ -67,6 +68,7 @@ def configuration(parent_package='', top_path=None):
           download_url=DOWNLOAD_URL,
           long_description=LONG_DESCRIPTION,
           zip_safe=False,  # the package can run out of an .egg file
+          cmdclass={"sdist": sdist},
           classifiers=[
               'Intended Audience :: Science/Research',
               'Intended Audience :: Developers',