README.md: Use matrix chat room

Signed-off-by: Andrei Gherzan <andrei@gherzan.ro>

README.md

@@ -5,7 +5,7 @@ Yocto BSP layer for the Raspberry Pi boards - <http://www.raspberrypi.org/>.
 [![Build Status](https://yocto-ci.resin.io/job/meta-raspberrypi1/badge/icon)](https://yocto-ci.resin.io/job/meta-raspberrypi1)
 [![Build Status](https://yocto-ci.resin.io/job/meta-raspberrypi2/badge/icon)](https://yocto-ci.resin.io/job/meta-raspberrypi2)
 [![Build Status](https://yocto-ci.resin.io/job/meta-raspberrypi3/badge/icon)](https://yocto-ci.resin.io/job/meta-raspberrypi3)
-[![Gitter chat](https://badges.gitter.im/gitterHQ/gitter.png)](https://gitter.im/agherzan/meta-raspberrypi)
+[![Matrix](https://img.shields.io/matrix/meta-raspberrypi:cub.icu.svg?server_fqdn=matrix.cub.icu)](https://matrix.to/#/#meta-raspberrypi:cub.icu)
 
 ## Quick links