docs: add link to DataFrames intro to improve SEO (#1176)

Co-authored-by: Tim Sweña (Swast) <[email protected]>

Author: Adam-Dupaski

README.rst

@@ -30,7 +30,8 @@ Documentation
 
 Getting started with BigQuery DataFrames
 ----------------------------------------
-Try the `BigQuery DataFrames quickstart <https://cloud.google.com/bigquery/docs/dataframes-quickstart>`_
+Read `Introduction to BigQuery DataFrames <https://cloud.google.com/bigquery/docs/bigquery-dataframes-introduction>`_
+and try the `BigQuery DataFrames quickstart <https://cloud.google.com/bigquery/docs/dataframes-quickstart>`_
 to get up and running in just a few minutes.