Document the known issues when BQ datasets are not in the US

[fedorov]

BQ datasets should be created in the US, otherwise:

• impossible to query across tables in different regions
• impossible to copy tables/datasets across some locations/regions
• error reporting in BQ is terrible and will not allow to figure out the underlying issue

[fedorov]

Solution to enable copy of datasets (not tables) across regions:

1. $ gcloud services list --available --project=$MY_PROJECT_ID | grep bigquery
2. $ gcloud services enable bigquerydatatransfer.googleapis.com --project=$MY_PROJECT_ID

Then need to re-initiate copy of the dataset, and give permissions to the BQ Data Transfer tool.

[fedorov]

Relevant docs https://cloud.google.com/bigquery/docs/copying-datasets