setup.py: add project_urls links
setup.py: add project_urls links

These additional URLs will be displayed on PyPI:
https://packaging.python.org/guides/distributing-packages-using-setuptools/#project-urls

Signed-off-by: Joshua Lock <edc229f50a11a11cdece0270af6320fb299dca1e@vmware.com>

secure-systems-lab/securesystemslib,secure-systems-lab/securesystemslib