Update README.rst

Author: ohmayr

README.rst

@@ -1,3 +1,6 @@
+.. _google-cloud-python: https://github.com/googleapis/google-cloud-python/tree/main/packages/pandas-gbq
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+
 pandas-gbq
 ==========
 
@@ -56,6 +59,10 @@ Upload a dataframe
 
     pandas_gbq.to_gbq(dataframe, "dataset.table")
 
+
+:**NOTE**: **This github repository is archived. The repository contents and history have moved to** `google-cloud-python`_.
+
+
 More samples
 ~~~~~~~~~~~~