Update README.md

Author: wangkuiyi

README.md

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 # Couler for Google Tekton
 
-Couler is a Python package allowing users to write [Tekton](https://github.com/tektoncd/pipeline) workflows in Python other than YAML.
+Couler is a Python package allowing users to write Argo and [Tekton](https://github.com/tektoncd/pipeline) workflows in Python other than YAML.
+
+This project is the Couler backend for Tekton.  The version for Argo is at [here](https://github.com/sql-machine-learning/sqlflow/blob/develop/python/couler/).
 
 Here is an example.  To the left is a Python program defining a Task and related TaskRun.  To the right is the equivalent YAML file.