Update chat badge from LF Energy Slack to Zulip

Author: danyill

README.md

@@ -3,7 +3,7 @@
 [![Build Status](https://travis-ci.org/openscd/open-scd.svg?branch=main)](https://travis-ci.org/openscd/open-scd)
 [![FOSSA Status](https://app.fossa.com/api/projects/git%2Bgithub.com%2Fopenscd%2Fopen-scd.svg?type=shield)](https://app.fossa.com/projects/git%2Bgithub.com%2Fopenscd%2Fopen-scd?ref=badge_shield)
 [![Built with open-wc recommendations](https://img.shields.io/badge/built%20with-open--wc-blue.svg)](https://github.com/open-wc)
-[![Slack LF Energy](https://img.shields.io/badge/LF%20Energy%20Slack-%20%23OpenSCD%20chat-purple?logo=slack&color=2aa198&labelColor=6c71c4)](https://lfenergy.slack.com/archives/C03LH7EUP34)
+[![Zulip Chat](https://img.shields.io/badge/Zulip%20-%20%23OpenSCD%20chat-purple?logo=zulip&color=2aa198&labelColor=6c71c4)](https://openscd.zulipchat.com/join/k3cyur3wx526tvafkjwubhjn)
 
 Open Substation Communication Designer is an editor for SCL files as described in `IEC 61850-6`.