Better explanation of `upload -d`

Hi, thanks for this!

`upload -d` is explained as

```
Use data flash from a file.
```

But it seems that without `-d`, with or without `-e` or `-u`, the `upload` command *always* uses a file, so it's unclear what the difference is.

Also, while I have a firmware image to upload, I don't know if it's encrypted or not. Is there a simple way to determine that?

Thanks for any help.