Add release notes project URL (#365)

Background info at https://github.com/pypa/warehouse/pull/7882

setup.py

@@ -46,5 +46,8 @@ setup(
         'License :: OSI Approved :: MIT License',
         'Programming Language :: Python :: 3.6',
         'Programming Language :: Python :: 3.7'
-    ]
+    ],
+    project_urls={
+        'Release notes': 'https://github.com/typeddjango/django-stubs/releases',
+    },
 )