Add shields.io badge for the documentation in the README

Author: DavideD

README.md

@@ -4,6 +4,7 @@
 [![Apache 2.0 license](https://img.shields.io/badge/License-APACHE%202.0-green.svg?logo=APACHE&style=flat)](https://opensource.org/licenses/Apache-2.0)
 [![Latest version on Maven Central](https://img.shields.io/maven-central/v/org.hibernate.reactive/hibernate-reactive-core.svg?label=Maven%20Central&logo=apache-maven&style=flat)](https://search.maven.org/search?q=g:%22org.hibernate.reactive%22)
 [![Developers stream on Zulip](https://img.shields.io/badge/zulip-join_chat-brightgreen.svg?logo=zulip&style=flat)](https://hibernate.zulipchat.com/#narrow/stream/205413-hibernate-reactive-dev)
+[![Hibernate Reactive documentation](https://img.shields.io/badge/Hibernate-Documentation-orange.svg?logo=Hibernate&style=flat)](https://hibernate.org/reactive/documentation/)
 
 # Hibernate Reactive