.arcconfig

repoview: improve documentation for `repo.filtered` method

I am sitting next to Joerg Sonnenberger and we are discussion his experience
with repoview. This first effect of this discussion is this documentation
clarification.

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