Mark clearly which keys can be imported

[szszszsz]

Mark clearly which keys can be imported, and for what models.
Potentially remove the additional description and link to the docs.nitrokey directly from the old docs:

• https://www.nitrokey.com/de/documentation/frequently-asked-questions-faq#can-i-backup-the-internal-keys

The FAQ says, that internal keys can be backupped (/regenerated) when it is done before the generation of Keys (technically probably setting a seed?). However, the FAQ then references a OpenPGP-specific section of the documentation. Does that mean that this is only possible for OpenPGP and not for others? (FIDO2, U2F …)? If so, FAQ should mention it

Source:

• https://support.nitrokey.com/t/use-token-for-more-than-1-account-on-same-domain-backupability-of-keys/3947