.arcconfig

discovery-helper: add an extra argument to generate only one repo

This is useful to generate left and right in parallel when dealing with very
large repositories.

{
    "conduit_uri": "https://phab.mercurial-scm.org/api",
    "repository.callsign": "HG",
    "arc.land.onto.default": "@",
    "base": "hg:.^"
}