pyrefly check error message does not state that single-file checking works

[AA-Turner]

I initially ran:

PS> pyrefly check
Thread panicked, shutting down: panicked at bin/main.rs:109:5:
Project-checking mode has not been implemented yet
Backtrace:
   0: <unknown>
   1: <unknown>
   2: <unknown>
   3: <unknown>
   4: <unknown>
   5: <unknown>
   6: <unknown>
   7: <unknown>
   8: <unknown>
   9: <unknown>
  10: <unknown>
  11: <unknown>
  12: <unknown>
  13: <unknown>
  14: BaseThreadInitThunk
  15: RtlUserThreadStart

Running with the path to a file does work, and produces type errors rather than Rust panics -- could the error message redirect users to supply a file or list of files to pyre check (and not print a backtrace?)

A