Problem with setup.py and requirements.txt

[citos88]

When I run tox I have problem with installing requirements.

Processing ./.tox/.tmp/package/1/django-discounts-0.1.0.zip
    ERROR: Command errored out with exit status 1:
     command: /home/citos88/projects/django-discounts/django-discounts/.tox/py36-django31/bin/python -c 'import sys, setuptools, tokenize; sys.argv[0] = '"'"'/tmp/pip-req-build-0qaa0txg/setup.py'"'"'; __file__='"'"'/tmp/pip-req-build-0qaa0txg/setup.py'"'"';f=getattr(tokenize, '"'"'open'"'"', open)(__file__);code=f.read().replace('"'"'\r\n'"'"', '"'"'\n'"'"');f.close();exec(compile(code, __file__, '"'"'exec'"'"'))' egg_info --egg-base /tmp/pip-pip-egg-info-jli2w2lu
         cwd: /tmp/pip-req-build-0qaa0txg/
    Complete output (5 lines):
    Traceback (most recent call last):
      File "<string>", line 1, in <module>
      File "/tmp/pip-req-build-0qaa0txg/setup.py", line 47, in <module>
        with open("./requirements.txt") as f:
    FileNotFoundError: [Errno 2] No such file or directory: './requirements.txt'

I found that I need add this line in MANIFEST.in include requirements.txt