docs: updates with a link to the canonical source of documentation (#620)

* updates main page with a link to the canonical source of documentation

* Update docs/index.rst

* Update docs/index.rst

Co-authored-by: Anthonios Partheniou <[email protected]>

---------

Co-authored-by: Anthonios Partheniou <[email protected]>

Author: chalmerlowe

docs/index.rst

@@ -13,6 +13,10 @@ with a shape and data types derived from the source table. Additionally,
 DataFrames can be inserted into new BigQuery tables or appended to existing
 tables.
 
+Note:  The canonical version of this documentation can always be found on the
+`googleapis.dev pandas-gbq site
+<https://googleapis.dev/python/pandas-gbq/latest/index.html>`__.
+
 .. note::
 
    To use this module, you will need a valid BigQuery account. Use the