Refer to 37signals blog post for alternative

According to the rationale at https://github.com/rails/rails/pull/7833#issuecomment-9141908, we should recommend new users to follow DHH's approach outlined at http://37signals.com/svn/posts/3113-how-key-based-cache-expiration-works.

This is the first step, and perhaps in the future we can write some specific recommendations out.