Add Slack badge

README.md

@@ -9,6 +9,7 @@ This is the Node.js binding to the
 [![Build Status](https://github.com/openzim/node-libzim/workflows/CI/badge.svg?branch=main)](https://github.com/openzim/node-libzim/actions?query=branch%3Amain)
 [![codecov](https://codecov.io/gh/openzim/node-libzim/branch/main/graph/badge.svg)](https://codecov.io/gh/openzim/node-libzim)
 [![CodeFactor](https://www.codefactor.io/repository/github/openzim/node-libzim/badge)](https://www.codefactor.io/repository/github/openzim/node-libzim)
+[![Join Slack](https://img.shields.io/badge/Join%20on%20Slack%20%23mwoffliner-2EB67D)](https://slack.kiwix.org)
 [![License: GPL v3](https://img.shields.io/badge/License-GPLv3-blue.svg)](https://www.gnu.org/licenses/gpl-3.0)
 
 ## Dependencies