LoongArch notification group

Github Label: O-loongarch
Ping command: @rustbot ping loongarch

This list will be used to ask for help both in diagnosing and testing LoongArch-related issues as well as suggestions on how to resolve interesting questions regarding our LoongArch support.

The group also has an associated Zulip channel (#t-compiler/loong-arch) where people can go to pose questions and discuss LoongArch-specific topics.

So, if you are interested in participating, please sign up for the LoongArch group! To do so, open a PR against the rust-lang/team repository. Just follow this example, but change the username to your own!