Add matrix haskell-tooling channel (haskell#2210)

Co-authored-by: Junyoung "Clare" Jang <[email protected]>

Author: jneira

docs/contributing/contributing.md

@@ -5,6 +5,7 @@ The Haskell tooling dream is near, we need your help!
 - Join [our IRC channel](https://web.libera.chat/?channels=#haskell-language-server) at `#haskell-language-server` on [`libera`](https://libera.chat/).
 - Follow the [Haskell IDE team twitter account](https://twitter.com/IdeHaskell) for updates and help.
 - Join the [#haskell-tooling channel](https://discord.com/channels/280033776820813825/505370075402862594/808027763868827659) in the Functional Programming discord server. You can join the server via [this invitation](https://discord.gg/9spEdTNGrD).
+- Join the [haskell-tooling channel](https://matrix.to/#/#haskell-tooling:matrix.org) in [matrix](https://matrix.org/).
 
 ## Building haskell-language-server