Suggest explicit mode of `'any` with `read-line`.

[jackfirth]

See racket/racket#4074. Resyntax could suggest replacing (read-line in) with (read-line in 'any) and (read-line) with (read-line (current-input-port) 'any). This technically changes behavior; a behavior-preserving transformation would be to use 'linefeed instead. The suggestion could document that 'linefeed is a bad default and to use it explicitly if 'any doesn't work.