Add reference to spring-batch-extensions

Author: scordio

README.md

@@ -1,3 +1,6 @@
+> [!IMPORTANT]  
+> This project is now part of [spring-projects/spring-batch-extensions](https://github.com/spring-projects/spring-batch-extensions).
+
 # Spring Batch Notion [![Maven Central](https://img.shields.io/maven-central/v/io.github.scordio/spring-batch-notion?label=Maven%20Central)](https://mvnrepository.com/artifact/io.github.scordio/spring-batch-notion) [![javadoc](https://javadoc.io/badge2/io.github.scordio/spring-batch-notion/javadoc.svg)](https://javadoc.io/doc/io.github.scordio/spring-batch-notion)
 
 [![CI](https://github.com/scordio/spring-batch-notion/actions/workflows/main.yml/badge.svg?branch=main)](https://github.com/scordio/spring-batch-notion/actions/workflows/main.yml?query=branch%3Amain)