Document `match.distance_weights` in autotagger docs

[snejus]

I'm slightly shocked that we don't seem to have documentation for the following configuration?

match:
    distance_weights:
        data_source: 2.0
        artist: 3.0
        album: 3.0
        media: 1.0
        mediums: 1.0
        year: 1.0
        country: 0.5
        label: 0.5
        catalognum: 0.5
        albumdisambig: 0.5
        album_id: 5.0
        tracks: 2.0
        missing_tracks: 0.9
        unmatched_tracks: 0.6
        track_title: 3.0
        track_artist: 2.0
        track_index: 1.0
        track_length: 2.0
        track_id: 5.0
        medium: 1.0