Replace slack with discord

README.md

@@ -42,6 +42,6 @@ All contributors are encouraged to read the [Ballerina Code of Conduct](https://
 ## Useful Links
 
 * Discuss about code changes of the Ballerina project in [ballerina-dev@googlegroups.com](mailto:ballerina-dev@googlegroups.com).
-* Chat live with us via our [Slack channel](https://ballerina.io/community/slack/).
+* Chat live with us via our [Discord server](https://discord.gg/ballerinalang).
 * Post all technical questions on Stack Overflow with the [#ballerina](https://stackoverflow.com/questions/tagged/ballerina) tag.
 * View the [Ballerina performance test results](performance/benchmarks/summary.md).