Bigquery Datatransfer: Add nox session docs (via synth).

[yoshi-automation]

This PR was generated using Autosynth. 🌈

Here's the log from Synthtool:

synthtool > Executing /tmpfs/src/git/autosynth/working_repo/bigquery_datatransfer/synth.py.
synthtool > Ensuring dependencies.
synthtool > Pulling artman image.
latest: Pulling from googleapis/artman
Digest: sha256:c58f4ec3838eb4e0718eb1bccc6512bd6850feaa85a360a9e38f6f848ec73bc2
Status: Image is up to date for googleapis/artman:latest
synthtool > Cloning googleapis.
synthtool > Running generator for google/cloud/bigquery/datatransfer/artman_bigquerydatatransfer.yaml.
synthtool > Generated code into /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/bigquerydatatransfer-v1.
synthtool > Copy: /home/kbuilder/.cache/synthtool/googleapis/google/cloud/bigquery/datatransfer/v1/transfer.proto to /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/bigquerydatatransfer-v1/google/cloud/bigquery_datatransfer_v1/proto/transfer.proto
synthtool > Copy: /home/kbuilder/.cache/synthtool/googleapis/google/cloud/bigquery/datatransfer/v1/datatransfer.proto to /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/bigquerydatatransfer-v1/google/cloud/bigquery_datatransfer_v1/proto/datatransfer.proto
synthtool > Placed proto files into /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/bigquerydatatransfer-v1/google/cloud/bigquery_datatransfer_v1/proto.
synthtool > Replaced 'from google.cloud.bigquery.datatransfer_v1.proto' in google/cloud/bigquery_datatransfer_v1/proto/datatransfer_pb2.py.
synthtool > Replaced 'from google.cloud.bigquery.datatransfer_v1.proto' in google/cloud/bigquery_datatransfer_v1/proto/datatransfer_pb2_grpc.py.
synthtool > Replaced 'google-cloud-bigquerydatatransfer' in google/cloud/bigquery_datatransfer_v1/gapic/data_transfer_service_client.py.
synthtool > Replaced 'import google.api_core.gapic_v1.method\n' in google/cloud/bigquery_datatransfer_v1/gapic/data_transfer_service_client.py.
.coveragerc
.flake8
MANIFEST.in
noxfile.py.j2
setup.cfg
Running session blacken
Creating virtualenv using python3.6 in /tmpfs/src/git/autosynth/working_repo/bigquery_datatransfer/.nox/blacken
pip install black
black google tests docs
reformatted /tmpfs/src/git/autosynth/working_repo/bigquery_datatransfer/google/cloud/__init__.py
reformatted /tmpfs/src/git/autosynth/working_repo/bigquery_datatransfer/google/__init__.py
reformatted /tmpfs/src/git/autosynth/working_repo/bigquery_datatransfer/google/cloud/bigquery_datatransfer.py
reformatted /tmpfs/src/git/autosynth/working_repo/bigquery_datatransfer/google/cloud/bigquery_datatransfer_v1/__init__.py
reformatted /tmpfs/src/git/autosynth/working_repo/bigquery_datatransfer/google/cloud/bigquery_datatransfer_v1/gapic/enums.py
reformatted /tmpfs/src/git/autosynth/working_repo/bigquery_datatransfer/google/cloud/bigquery_datatransfer_v1/gapic/data_transfer_service_client_config.py
reformatted /tmpfs/src/git/autosynth/working_repo/bigquery_datatransfer/google/cloud/bigquery_datatransfer_v1/gapic/transports/data_transfer_service_grpc_transport.py
reformatted /tmpfs/src/git/autosynth/working_repo/bigquery_datatransfer/google/cloud/bigquery_datatransfer_v1/proto/datatransfer_pb2_grpc.py
reformatted /tmpfs/src/git/autosynth/working_repo/bigquery_datatransfer/google/cloud/bigquery_datatransfer_v1/proto/transfer_pb2_grpc.py
reformatted /tmpfs/src/git/autosynth/working_repo/bigquery_datatransfer/google/cloud/bigquery_datatransfer_v1/types.py
reformatted /tmpfs/src/git/autosynth/working_repo/bigquery_datatransfer/tests/system/gapic/v1/test_system_data_transfer_service_v1.py
reformatted /tmpfs/src/git/autosynth/working_repo/bigquery_datatransfer/google/cloud/bigquery_datatransfer_v1/gapic/data_transfer_service_client.py
reformatted /tmpfs/src/git/autosynth/working_repo/bigquery_datatransfer/tests/unit/gapic/v1/test_data_transfer_service_client_v1.py
reformatted /tmpfs/src/git/autosynth/working_repo/bigquery_datatransfer/google/cloud/bigquery_datatransfer_v1/proto/transfer_pb2.py
reformatted /tmpfs/src/git/autosynth/working_repo/bigquery_datatransfer/google/cloud/bigquery_datatransfer_v1/proto/datatransfer_pb2.py
All done! ✨ 🍰 ✨
15 files reformatted, 4 files left unchanged.
Session blacken was successful.
synthtool > Cleaned up 2 temporary directories.
synthtool > Wrote metadata to synth.metadata.

[busunkim96]

Ignoring failing tests in unrelated APIs: BigQuery, Firestore, Logging, OS Login, Phishing Protection, Storage.

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