docs: Add cross-referencing for gRPC (#22)

mkdocs.yml

@@ -116,9 +116,9 @@ plugins:
             show_source: true
             signature_crossrefs: true
           import:
-            # TODO(cookiecutter): You might want to add other external references here
             # See https://mkdocstrings.github.io/python/usage/#import for details
             - https://docs.python.org/3/objects.inv
+            - https://grpc.github.io/grpc/python/objects.inv
             - https://typing-extensions.readthedocs.io/en/stable/objects.inv
   # Note this plugin must be loaded after mkdocstrings to be able to use macros
   # inside docstrings. See the comment in `docs/_scripts/macros.py` for more