DOC: synchronize docs changes with pandas (#190)
DOC: synchronize docs changes with pandas (#190)

The docs needs some corrections in order to pass the Pandas docs linter
in https://github.com/pandas-dev/pandas/pull/21628
pydata/pandas-gbq,googleapis/python-bigquery-pandas,pydata/pydata-google-auth,googleapis/python-bigquery-pandas,pydata/pandas-gbq