security/opkssh: Add note for jails

security/opkssh: New port: Tool which enables SSH to be used with OpenID Connect

opkssh is a tool which enables ssh to be used with OpenID Connect
allowing SSH access to be managed via identities like alice@example.com
instead of long-lived SSH keys. It does not replace SSH, but instead
generates SSH public keys containing PK Tokens and configures sshd
to verify them. These PK Tokens contain standard OpenID Connect ID
Tokens. This protocol builds on the OpenPubkey which adds user
public keys to OpenID Connect without breaking compatibility with
existing OpenID Provider.