chore: add Discord badge to README

Author: bjarn

README.md

@@ -4,6 +4,7 @@
 [![GitHub Tests Action Status](https://img.shields.io/github/actions/workflow/status/lettermint/lettermint-php/run-tests.yml?branch=main&label=tests&style=flat-square)](https://github.com/lettermint/lettermint-php/actions?query=workflow%3Arun-tests+branch%3Amain)
 [![GitHub Code Style Action Status](https://img.shields.io/github/actions/workflow/status/lettermint/lettermint-php/fix-php-code-style-issues.yml?branch=main&label=code%20style&style=flat-square)](https://github.com/lettermint/lettermint-php/actions?query=workflow%3A"Fix+PHP+code+style+issues"+branch%3Amain)
 [![Total Downloads](https://img.shields.io/packagist/dt/lettermint/lettermint-php.svg?style=flat-square)](https://packagist.org/packages/lettermint/lettermint-php)
+[![Join our Discord server](https://img.shields.io/discord/1305510095588819035?logo=discord&logoColor=eee&label=Discord&labelColor=464ce5&color=0D0E28&cacheSeconds=43200)](https://lettermint.co/r/discord)
 
 Integrate Lettermint in your PHP project.