project_setup.md out of sync

[sverhoeven]

• says setup.py` in the `install\_requires while it is now in setup.cfg
• says pipy instead of pypi
• test_lint.py is gone
• python setup.py test does not work, needs pip install -e .[dev] first
• Travis section should be replaced with GH actions
• Fix README to ./README.md
• package version is stored in a single place not true

[jspaaks]

Updated bullet list above to be checkmarkable

[jspaaks]

PR #208 fixes the remaining 2 items above

[fdiblen]

fixed by #208