Change note in alter agent section

Different methods have different requirements

README.md

@@ -1979,8 +1979,9 @@ export SSH_AUTH_SOCK=$(gpgconf --list-dirs agent-ssh-socket)
 gpgconf --launch gpg-agent
 ```
 
-Note that `SSH_AUTH_SOCK` normally only needs to be set on the *local* laptop (workstation), where the YubiKey is plugged in.  On the *remote* server that we SSH into, `ssh` will automatically set `SSH_AUTH_SOCK` to something like `/tmp/ssh-mXzCzYT2Np/agent.7541` when we connect.  We therefore do **NOT** manually set `SSH_AUTH_SOCK` on the server - doing so would break [SSH Agent Forwarding](#remote-machines-gpg-agent-forwarding).
+Note that if you use `ForwardAgent` for ssh-agent forwarding, `SSH_AUTH_SOCK` only needs to be set on the *local* laptop (workstation), where the YubiKey is plugged in.  On the *remote* server that we SSH into, `ssh` will automatically set `SSH_AUTH_SOCK` to something like `/tmp/ssh-mXzCzYT2Np/agent.7541` when we connect.  We therefore do **NOT** manually set `SSH_AUTH_SOCK` on the server - doing so would break [SSH Agent Forwarding](#remote-machines-ssh-agent-forwarding).
 
+If you use `S.gpg-agent.ssh` (see [SSH Agent Forwarding](#remote-machines-ssh-agent-forwarding) for more info), `SSH_AUTH_SOCK` should also be set on the *remote*. However, `GPG_TTY` should not be set on the *remote*, explanation specified in that section.
 
 ## Copy public key