Added reference to the JavaDoc

Author: rcardin

README.md

@@ -2,6 +2,7 @@
 ![GitHub Workflow Status (with branch)](https://img.shields.io/github/actions/workflow/status/rcardin/assertj-arrow-core/ci.yml?branch=main)
 ![Maven Central](https://img.shields.io/maven-central/v/in.rcard/assertj-arrow-core)
 ![GitHub release (latest by date)](https://img.shields.io/github/v/release/rcardin/assertj-arrow-core)
+[![javadoc](https://javadoc.io/badge2/in.rcard/assertj-arrow-core/javadoc.svg)](https://javadoc.io/doc/in.rcard/assertj-arrow-core)
 <a href="https://pinterest.github.io/ktlint/"><img src="https://img.shields.io/badge/code%20style-%E2%9D%A4-FF4081.svg" alt="ktlint"></a>
 
 # assertj-arrow-core