all-instructions shows up in google search results

[SwartzCr]

people searching for certbot instructions sometimes get routed to certbot.eff.org/all-instructions which is a terrible user experience. It can even show up above the plain certbot.eff.org page in search results. We should either remove SEO for that page (if there is one) or add a robots.txt to that page to prevent it from being indexed, so that people land on the interactive page