enhancement: add some metadata to provide extra info in its PyPI page

Add some metadata (project_urls) to provide extra info in its PyPI page.

Signed-off-by: Satoru SATOH <satoru.satoh@gmail.com>

setup.cfg

@@ -39,6 +39,12 @@ classifiers =
   Topic :: Software Development :: Quality Assurance
   Topic :: Software Development :: Testing
 
+project_urls =
+  Documentation = https://yamllint.readthedocs.io
+  Download = https://pypi.org/project/yamllint/#files
+  Bug Tracker = https://github.com/adrienverge/yamllint/issues
+  Source Code = https://github.com/adrienverge/yamllint
+
 [options]
 packages = find: