Mention the new key types, the ~/.ssh/id_ecdsa_sk file, ssh's
SecurityKeyProvider keyword, the SSH_SK_PROVIDER environment variable,
and ssh-keygen's new -w and -x options.
Copy the ssh-sk-helper man page from ssh-pkcs11-helper with minimal
substitutions.
ok djm@
OpenBSD-Commit-ID: ef2e8f83d0c0ce11ad9b8c28945747e5ca337ac4
naddy@openbsd.org