docs: use a short-link to BigQuery DataFrames (#773)

Author: tswast

docs/index.rst

@@ -23,8 +23,8 @@ Note:  The canonical version of this documentation can always be found on the
    `BigQuery sandbox <https://cloud.google.com/bigquery/docs/sandbox>`__ to
    try the service for free.
 
-   Also, consider using `BigQuery DataFrames
-   <https://cloud.google.com/bigquery/docs/bigquery-dataframes-introduction>`__
+   Also, consider using BigQuery DataFrames 
+   (`bit.ly/bigframes-intro <https://bit.ly/bigframes-intro>`__)
    to process large results with pandas compatible APIs with transparent SQL
    pushdown to BigQuery engine. This provides an opportunity to save on costs
    and improve performance.

pandas_gbq/gbq.py

@@ -493,8 +493,7 @@ def _download_results(
                 num_gib = num_bytes / pandas_gbq.constants.BYTES_IN_GIB
                 warnings.warn(
                     f"Recommendation: Your results are {num_gib:.1f} GiB. "
-                    "Consider using BigQuery DataFrames "
-                    "(https://cloud.google.com/bigquery/docs/bigquery-dataframes-introduction) "
+                    "Consider using BigQuery DataFrames (https://bit.ly/bigframes-intro)"
                     "to process large results with pandas compatible APIs with transparent SQL "
                     "pushdown to BigQuery engine. This provides an opportunity to save on costs "
                     "and improve performance. "