message: Add doc entry for BigQuery support
  closes
diff: @@ -320,6 +320,8 @@ Here's a list of some of the recommended packages.
  +---------------+-------------------------------------+-------------------------------------------------+
  | Kylin | ``pip install kylinpy`` | ``kylin://`` |
  +---------------+-------------------------------------+-------------------------------------------------+
  +| BigQuery | ``pip install pybigquery`` | ``bigquery://`` |
  ++---------------+-------------------------------------+-------------------------------------------------+
  Note that many other database are supported, the main criteria being the
  existence of a functional SqlAlchemy dialect and Python driver. Googling
  