doc: add arm64 macOS as experimental

PR-URL: https://github.com/nodejs/node/pull/36189
Refs: https://github.com/nodejs/build/issues/2474


Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Ash Cripps <acripps@redhat.com>
Reviewed-By: David Carlier <devnexen@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Pranshu Srivastava <rexagod@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>