Create decent user experience for operators of candidate subjects for certification #212

(Disclaimer: issue title is not perfect, I know...)

Problem: at the moment, you have to dig to find out what you need to do to become KaaS or IaaS certified. The information is there, but it is distributed and not easy to find.

For example, going from the scs.community homepage:

• first click "Documentation" (there is not top level "Standards" link)
• go to "Standards" -> "Certification"
  • some people might not even get here, because they except this kind of information under "For Operators" ?
• in the section "Becoming certified" you'll get directed to "Regulations for achieving SCS-compatible certification", which is itself a standard.
• regulation no. 2 has a link to the /Tests directory in the standards repository
  • the README has all infos, but it is way too technical

This should be improved:

• The "Standards" page could have better visibility on its own (e.g., in "Discover SCS" or next to "Documentation" on the SCS landing page).
• Make "How to become certified" a top level menu entry on the "Standards" page (and maybe also on the "For Operators" page?)
  • using the reference implementation? -> you're already good
  • using sth else? -> collection of links to implementation notes, guides, blog posts
• Include an easy to follow step-by-step guide for the IaaS and KaaS conformance checks against a cloud.

UPDATE: There are some recent improvements (new implementation notes) in the standards repository which should be considered: SovereignCloudStack/standards#631 (already merged) and SovereignCloudStack/standards#643 (work in progress).