Request: Erlang example

https://buck2.build/docs/api/rules/#erlang_app describes use of the `erlang_application` macro, however this seems to implicity rely on the existence of `toolchains//:erlang-default`. The `@prelude//toolchains` directory does not seem to contain any kind of erlang toolchain however. It would be nice to have a complete basic erlang application example for Buck2.