.arcconfig

gitweb: add link to graph

error.tmpl wasn't consistent with other templates in gitweb in
that it was missing a "graph" link. This commit makes it consistent.

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