Add link to Stripe's Discord server to the readme (#2178)

Author: remi-stripe

README.md

@@ -4,6 +4,9 @@
 [![JavaDoc](http://img.shields.io/badge/javadoc-reference-blue.svg)](https://stripe.dev/stripe-java)
 [![Build Status](https://github.com/stripe/stripe-java/actions/workflows/ci.yml/badge.svg?branch=master)](https://github.com/stripe/stripe-java/actions?query=branch%3Amaster)
 
+> [!TIP]
+> Want to chat live with Stripe engineers? Join us on our [Discord server](https://stripe.com/go/discord/java).
+
 The official [Stripe][stripe] Java client library.
 
 ## Installation