`faircode profile --reference` help text says CSV-only but accepts any supported format

[yakew7]

_read_or_exit() in faircode/cli.py is used for both the main dataset argument and --reference, so the reference baseline file already goes through the same loaders_extra.read_table() and supports .tsv/.xlsx/.json/.parquet - but the argparse help text still reads:

--reference PATH  score against a reference baseline CSV (columns: column,group,share)

Small, low-risk doc fix: drop "CSV" (or say "file") so the help text matches actual behavior.