doc: added docs for defaultDataset (#749)
doc: added docs for defaultDataset (#749)

Co-authored-by: Steffany Brown <b467a80c12ede44da5e2e54f18846e75da932d0e@users.noreply.github.com>
Co-authored-by: sofisl <db5f31dcffac94c616d6f139fc6a9d43079218ec@users.noreply.github.com>
googleapis/nodejs-bigquery,googleapis/nodejs-bigquery,googleapis/nodejs-bigquery