.arcconfig

graphlog: document what "_" and "*" mean

Documenting "*" should've been a part of 9b3f95d9783d, but I somehow didn't
notice that the symbols are explained in the command's help text.

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