display available formatters on a faulty "treefmt --formatters" call

[teto]

Is your feature request related to a problem? Please describe.

I configure the team's treefmt via treefmt-nix but the team doesnt know anything about treefmt, they run it via make lint or an equivalent. I wanted to tell them they could run treefmt -f FORMATTER but they wouldn't know which ones are available.

Describe the solution you'd like
To help discover currently configured formatters, it could be nice to list the formatters somehow. I believe this could be a good candidate, right now we have:

❯ treefmt -f
error: a value is required for '--formatters <FORMATTERS>' but none was supplied

For more information, try '--help'.

and I would suggest:

❯ treefmt -f
error: a value is required for '--formatters <FORMATTERS>' but none was supplied.

Configured formatters:
- ormolu
- black

For more information, try '--help'.

Describe alternatives you've considered

Additional context