Fixed link to GitHub Enterprise benefits post

Sorry, found one other link that was amiss (and you closed the other PR too fast). The link to Brandon's usecase (GitHub Enterprise benefits) was broken, I guess after the change to Jekyll/Octopress. I fixed it (but just pointed to the external link, i.e. http://teach.github.com/articles/github-enterprise-features/), maybe there's a better way to link to internal docs?