feat: Add Discord badge in README.md (TheAlgorithms#2196)

Author: Panquesito7

README.md

@@ -3,6 +3,7 @@
 # The Algorithms - Java
 [![Build Status](https://api.travis-ci.com/TheAlgorithms/Java.svg?branch=master)](https://travis-ci.com/TheAlgorithms/Java) 
 [![Donate](https://img.shields.io/badge/Donate-PayPal-green.svg)](https://www.paypal.me/TheAlgorithms/100)
+[![Discord chat](https://img.shields.io/discord/808045925556682782.svg?logo=discord&colorB=7289DA&style=flat-square)](https://discord.gg/c7MnfGFGa6) 
 [![Gitter chat](https://img.shields.io/badge/Chat-Gitter-ff69b4.svg?label=Chat&logo=gitter&style=flat-square)](https://gitter.im/TheAlgorithms) 
 
 You can run and edit the algorithms or contribute to them using Gitpod.io, a free online development environment, with a single click.