Added Discord badge

Author: dfahlander

README.md

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 # Dexie.js
 
-[![NPM Version][npm-image]][npm-url] ![Build Status](https://github.com/dexie/Dexie.js/actions/workflows/main.yml/badge.svg)
+[![NPM Version][npm-image]][npm-url] ![Build Status](https://github.com/dexie/Dexie.js/actions/workflows/main.yml/badge.svg) [![Join our Discord](https://img.shields.io/discord/1328303736363421747?label=Discord&logo=discord&style=badge)](https://discord.gg/huhre7MHBF)
 
 Dexie.js is a wrapper library for indexedDB - the standard database in the browser. https://dexie.org.