Include LICENSE in PyPI tarball

[kwshi]

This project uses the BSD 3-clause license, which requires that the license be distributed with all copies of the source code:

  Redistributions of source code must retain the above copyright notice, this
  list of conditions and the following disclaimer.

The PyPI source tarball does not include such a copy of the license:

> curl -fsSL 'https://files.pythonhosted.org/packages/source/c/click-default-group/click-default-group-1.2.2.tar.gz' | tar -tz
click-default-group-1.2.2/
click-default-group-1.2.2/PKG-INFO
click-default-group-1.2.2/README.md
click-default-group-1.2.2/click_default_group.egg-info/
click-default-group-1.2.2/click_default_group.egg-info/PKG-INFO
click-default-group-1.2.2/click_default_group.egg-info/SOURCES.txt
click-default-group-1.2.2/click_default_group.egg-info/dependency_links.txt
click-default-group-1.2.2/click_default_group.egg-info/requires.txt
click-default-group-1.2.2/click_default_group.egg-info/top_level.txt
click-default-group-1.2.2/click_default_group.py
click-default-group-1.2.2/setup.cfg
click-default-group-1.2.2/setup.py

That makes it difficult/impossible to legally include in third-party/OS package repositories, which require packaged code to be distributed in a license-compliant manner. It would be great if the PyPI tarball could be updated to include the license!