loongson/pypi: links for protobuf

INFO: Because this project isn't in the mirror_whitelist, no releases from root/pypi are included.

loongson/pypi protobuf-3.17.3-py2.py3-none-any.whl
loongson/pypi protobuf-3.14.0-py2.py3-none-any.whl
loongson/pypi protobuf-3.13.0-py2.py3-none-any.whl
loongson/pypi protobuf-3.12.2-py2.py3-none-any.whl
loongson/pypi protobuf-3.10.0-py2.py3-none-any.whl
loongson/pypi protobuf-3.6.1-py2.py3-none-any.whl