Bug report

Bug summary

A LICENSE file is not included in published PyPI packages. This makes pip-licenses unable to find a license file when generating a license report.

Code for reproduction

$ pip install pip-licenses matplotlib
$ pip-licenses --from=mixed --format=plain-vertical --with-license-file --no-license-path
...
matplotlib
3.3.1
Python Software Foundation License
UNKNOWN
...

Expected outcome

pip-licenses would find a LICENSE file when it inspects the unpacked wheel and print it rather than printing UNKNOWN. Newer versions of setuptools look in the root directory of a project for LICENSE files when they build, but in this project the LICENSE files are in a subdirectory, so they will need to be explicitly added using the license_files option to setuptools.setup.