Add source code and issue tracker links.

Since we're no longer providing an email address for the maintainer
group (and we want folks to use the issue tracker anyway) let's make
sure that the source code and issue tracker are listed in the package
metadata.

setup.py

@@ -28,6 +28,12 @@
     'author_email': 'wim@hidof.com, dthomas@osrfoundation.org',
     'maintainer': 'ROS Infrastructure Team',
     'url': 'http://wiki.ros.org/rosdistro',
+    'project_urls': {
+        'Source code':
+        'https://github.com/ros-infrastructure/rosdistro',
+        'Issue tracker':
+        'https://github.com/ros-infrastructure/rosdistro/issues',
+    },
     'keywords': ['ROS'],
     'classifiers': [
         'Programming Language :: Python',