readme: add discord to readme (#4533)

* readme: add discord to readme

Signed-off-by: Marko Baricevic <marbar3778@yahoo.com>

* add our id

README.md

@@ -9,7 +9,7 @@ Or [Blockchain](<https://en.wikipedia.org/wiki/Blockchain_(database)>), for shor
 [![version](https://img.shields.io/github/tag/tendermint/tendermint.svg)](https://github.com/tendermint/tendermint/releases/latest)
 [![API Reference](https://camo.githubusercontent.com/915b7be44ada53c290eb157634330494ebe3e30a/68747470733a2f2f676f646f632e6f72672f6769746875622e636f6d2f676f6c616e672f6764646f3f7374617475732e737667)](https://godoc.org/github.com/tendermint/tendermint)
 [![Go version](https://img.shields.io/badge/go-1.13-blue.svg)](https://github.com/moovweb/gvm)
-[![riot.im](https://img.shields.io/badge/riot.im-JOIN%20CHAT-green.svg)](https://riot.im/app/#/room/#tendermint:matrix.org)
+[![Discord](https://img.shields.io/discord/669268347736686612.svg)](https://discord.gg/AzefAFd)  
 [![license](https://img.shields.io/github/license/tendermint/tendermint.svg)](https://github.com/tendermint/tendermint/blob/master/LICENSE)
 [![](https://tokei.rs/b1/github/tendermint/tendermint?category=lines)](https://github.com/tendermint/tendermint)