add deprecation notice (#76)

README.md

@@ -3,6 +3,11 @@
 
 # GitHub Action for training Machine Learning Models using Azure
 
+## Deprecation notice
+
+This Action is deprecated. Instead, consider using the [CLI (v2)](https://docs.microsoft.com/azure/machine-learning/how-to-configure-cli) to manage and interact with Azure Machine Learning jobs (runs) in GitHub Actions.
+
+**Important:** The CLI (v2) is not recommended for production use while in preview.
 
 ## Usage