error-message change to `cut`

[Tornax O7]

Dear Sir or Madam,
I've a little suggestion for the `cut` tool. If I execute

```
echo "test" | cut -d s -c 1
```
then I'm getting the following error message:

```
cut: an input delimiter may be specified only when operating on fields
Try 'cut --help' for more information.
```

It took me some time to understand that the word `field` is referring to
the option `-f` for `fields`. It would be nice (at least in my opinion) to
add a little note that you're meaning the `-f` option. Something like this:

```
cut: an input delimiter may be specified only when operating on fields (the
`-f` option)
Try 'cut --help' for more information.
```

or:

```
cut: the `-d` option can only be used in combination with the `-f` option
Try 'cut --help' for more information.
```

Best Regards
Tornax