DOC: cross-reference to_gbq and read_gbq

Author: tswast

pandas/core/frame.py

@@ -1187,6 +1187,7 @@ def to_gbq(
         See Also
         --------
         pandas_gbq.to_gbq : This function in the pandas-gbq library.
+        pandas.read_gbq : Read a DataFrame from Google BigQuery.
         """
         from pandas.io import gbq
         return gbq.to_gbq(

pandas/io/gbq.py

@@ -89,6 +89,7 @@ def read_gbq(
     See Also
     --------
     pandas_gbq.read_gbq : This function in the pandas-gbq library.
+    pandas.DataFrame.to_gbq : Write a DataFrame to Google BigQuery.
     """
     pandas_gbq = _try_import()
     return pandas_gbq.read_gbq(