Add project URLs to setup.cfg

Adding project URLs (especially source code URL) makes it easier for dependency management tools (like Renovate).

Author: tlinhart

setup.cfg

@@ -7,6 +7,10 @@ long_description_content_type = text/plain
 author           = Jupyter Development Team
 author_email     = [email protected]
 url              = https://jupyter.org
+project_urls     =
+    Documentation = https://jupyter-core.readthedocs.io/
+    Source        = https://github.com/jupyter/jupyter_core
+    Tracker       = https://github.com/jupyter/jupyter_core/issues
 license          = BSD-3-Clause
 license_file     = COPYING.md
 classifiers      =