Include license file in the generated wheel package

[jdufresne]

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/user_guide.html#including-license-files-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.

Contribution checklist:

(also see CONTRIBUTING.rst for details)

• wrote descriptive pull request text
• added/updated test(s) N/A
• updated/extended the documentation N/A
• added relevant issue keyword
  in message body
• added news fragment in changelog folder
  • fragment name: <issue number>.<type>.rst for example (588.bugfix.rst)
  • <type> is must be one of bugfix, feature, deprecation,breaking, doc, misc
  • if pr has no issue: consider creating one first or change it to the pr number after creating the pr
  • "sign" fragment with "by @"
  • please use full sentences with correct case and punctuation, for example: "Fix issue with non-ascii contents in doctest text files - by :user:superuser."
  • also see examples
• added yourself to CONTRIBUTORS (preserving alphabetical order)

[ssbarnea]

I don't personally like updating unrelated files in a change that mentions something else.
It means that I should add myself to contributors document, even if I fix a missing comma?

Anyway, I am not aware about any policy that would forbit that so +1

[jdufresne]

If you're saying I shouldn't add my name to CONTRIBUTORS then I was merely following the contributing instructions in the PR template. So if that is incorrect, perhaps that could be updated.

Either way, I've rebased so my name is no longer being added as part of this change (it was included in a previous PR)

[gaborbernat]

We have no change amount needed to add it. It's fine to be added 👍 I'm not sure about this change, isn't it already added by setup.py? Does this only adds a meta field in the output? What is the expected change here?

[jdufresne]

Before this change, the .whl file created by the command python setup.py bdist_wheel contains the following files:

tox/cli.py
tox/interpreters.py
tox/_pytestplugin.py
tox/constants.py
tox/session.py
tox/_quickstart.py
tox/__init__.py
tox/util.py
tox/config.py
tox/exception.py
tox/hookspecs.py
tox/venv.py
tox/version.py
tox/result.py
tox/__main__.py
tox/package/__init__.py
tox/package/view.py
tox/package/builder/isolated.py
tox/package/builder/__init__.py
tox/package/builder/legacy.py
tox-3.5.4.dev6+g2ef9c88.dist-info/DESCRIPTION.rst
tox-3.5.4.dev6+g2ef9c88.dist-info/entry_points.txt
tox-3.5.4.dev6+g2ef9c88.dist-info/metadata.json
tox-3.5.4.dev6+g2ef9c88.dist-info/top_level.txt
tox-3.5.4.dev6+g2ef9c88.dist-info/WHEEL
tox-3.5.4.dev6+g2ef9c88.dist-info/METADATA
tox-3.5.4.dev6+g2ef9c88.dist-info/RECORD

After this change it now also contains the file:

tox-3.5.4.dev7+gadf5680.dist-info/LICENSE.txt

So, now the LICENSE file is distributed with the .whl package. This helps communicate the full license to library users and helps hold them accountable to it. When a wheel package is installed, this LICENSE.txt fille will be copied to library's *.dist-info/ directory.

Further, the license contains the text:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

The wheel package is a copy of the software. Therefore, it should contain the LICENSE text with its copyright.