Passphrase prompt when adding pgp key is unclear

I was trying to import a key using `keybase pgp select` and after choosing a key and entering the passphrase for the secret key I got another passphrase prompt:

```
Please enter the passphrase to unluck the secret key for: Device ""

Reason: sign new key:
```

It was really unclear to me what it was asking for. Eventually I found that it seemed to have been asking for my keybase passphrase. Could this be made more clear?

Start by reproducing the `keybase pgp select` flow through key selection and the second passphrase prompt. Clarify the prompt so it identifies which passphrase is required, and verify that the resulting wording matches the intended request.

Written by the indexing model from the issue text.