Add SSH example to README.md

[mpenning]

Arguably, the single-biggest use-case for any expect library is automating SSH logins. I am successfully doing this with ssh_logger but it took a while to grok all the corners of solving the problem. I spent a long time trying to detect SSH password: prompts with go-expect until I realized it just could not be done; you have to use sshpass instead.

I think other people would benefit from this use-case. Is there an interest in updating README.md with this information?