Add matrix link

Author: MabezDev

README.md

@@ -2,6 +2,8 @@
 
 This fork enables projects to be built for the ESP32 and ESP8266 using [espressif's llvm fork](https://github.com/espressif/llvm-xtensa). The [esp-rs](https://github.com/esp-rs) organization has been formed to develop runtime, pac and hal crates for the esp32 and eventually esp8266.
 
+Join in on the discussion: https://matrix.to/#/#esp-rs:matrix.org!
+
 ## Using this fork
 
 The [quickstart repo](https://github.com/MabezDev/xtensa-rust-quickstart) has more information on how to build this fork and use it to build xtensa compatible code.