Add Discord badge

Author: hkalexling

README.md

@@ -2,7 +2,7 @@
 
 # Mango
 
-[![Patreon](https://img.shields.io/badge/support-patreon-brightgreen?link=https://www.patreon.com/hkalexling)](https://www.patreon.com/hkalexling) ![Build](https://github.com/hkalexling/Mango/workflows/Build/badge.svg) [![Gitter](https://badges.gitter.im/mango-cr/mango.svg)](https://gitter.im/mango-cr/mango?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge)
+[![Patreon](https://img.shields.io/badge/support-patreon-brightgreen?link=https://www.patreon.com/hkalexling)](https://www.patreon.com/hkalexling) ![Build](https://github.com/hkalexling/Mango/workflows/Build/badge.svg) [![Gitter](https://badges.gitter.im/mango-cr/mango.svg)](https://gitter.im/mango-cr/mango?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge) [![Discord](https://img.shields.io/discord/855633663425118228?label=discord)](http://discord.com/invite/ezKtacCp9Q)
 
 Mango is a self-hosted manga server and reader. Its features include