Provide example use cases for IdentityAgent

[dkocher]

We provide interoperability with the IdentityAgent configuration directive from OpenSSH with iterate-ch/cyberduck#12710. Use cases should be documented

• [ ] Integration with 1Password using IdentityAgent ~/.1password/agent.sock. See also #192.
• [ ] Support for YubiKey using [yubikey-agent](https://github.com/FiloSottile/yubikey-agent
• [ ] Support for YubiKey using gpg-agent (IdentityAgent ~/.gnupg/S.gpg-agent.ssh)
• [ ] Interoperability with SSH Agent Powered by Secure Enclave

Pages

• [ ] https://docs.cyberduck.io/protocols/sftp/

[dkocher]

See also #112.