- This makes black wheels to be tagged as py3 default
- `python_requires=">=3.6"` ensures we are >= 3.6
Test:
```
python3 -m venv /tmp/build_black
/tmp/build_black/bin/pip install --upgrade pip setuptools wheel
/tmp/build_black/bin/python setup.py bdist_wheel
...
black-19.10b1.dev53+g81bf9bb.d20200508-py3-none-any.whl
```
Addresses #1385
The wheel package format supports including the license file. This is
done using the [metadata] section in the setup.cfg file. For additional
information on this feature, see:
https://wheel.readthedocs.io/en/stable/index.html#including-the-license-in-the-generated-wheel-file
Helps project comply with its own license:
> The above copyright notice and this permission notice shall be
> included in all copies or substantial portions of the Software.
