Update package metadata to reflect backport

The previous package metadata was assuming that the module was itself in
the standard library, but it is preferable for this to refer to the
backport itself.

setup.cfg

@@ -4,7 +4,7 @@ version = attr:backports.zoneinfo._version.__version__
 description = Backport of the standard library zoneinfo module
 long_description = file: README.md
 long_description_content_type = text/markdown
-url = https://github.com/python/cpython
+url = https://github.com/pganssle/zoneinfo
 author = Python Software Foundation
 author_email = [email protected]
 license = Apache-2.0
@@ -20,8 +20,9 @@ classifiers =
     Programming Language :: Python :: 3 :: Only
     Programming Language :: Python :: 3.8
 project_urls =
-    Bug Reports = https://bugs.python.org
-    Source = https://github.com/python/cpython
+    Source = https://github.com/pganssle/zoneinfo
+    Documentation = https://zoneinfo.readthedocs.io/en/latest/
+    Bug Reports = https://github.com/pganssle/zoneinfo/issues
 
 [options]
 packages = find: