Add to settings TOC and fix SSL page

I noticed when I landed here: https://docs.gitlab.com/omnibus/settings/ssl.html that many notes didn't render well when published.

I also noticed that I couldn't access the page from: https://docs.gitlab.com/omnibus/settings/README.html, so I added SSL and others to it. Please check they're ok to be there.

CC @marcel.amirault.