Update README.md

Author: kontent-ai-bot

README.md

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+> [!Warning]
+> Deprecation Notice: This repository is no longer maintained.
+>
+> We encourage you to explore our latest solution [Kickstart React GraphQL App](https://github.com/kontent-ai/kickstart-react-graphql-app)
+
 # Kontent.ai Sample app GraphQL React
 
 [![Node.js CI](https://github.com/kontent-ai/sample-app-graphql-react/actions/workflows/node.js.yml/badge.svg)](https://github.com/kontent-ai/sample-app-graphql-react/actions/workflows/node.js.yml)