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 <[email protected]>

Author: joshuagl

setup.py

@@ -108,6 +108,10 @@
     'Topic :: Security',
     'Topic :: Software Development'
   ],
+  project_urls={
+    'Source': 'https://github.com/theupdateframework/tuf',
+    'Issues': 'https://github.com/theupdateframework/tuf/issues'
+  },
   python_requires=">=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*, !=3.4.*, <4",
   install_requires = [
     'iso8601>=0.1.12',