Add `What's next/Beginner's cheat sheet` page into `Getting started` section

[Kostov6]

What would you like to be added: As the Getting started section has a nice progression order after finishing it a beginner has no idea what to read next / is not familiar with the website structure. It would be nice to have a introduction of the overall website structure and to highlight core links/documents that can not be inferred by the structure alone. For example the Glossary document and the referenced Kubernetes glossary document are very good resources for a beginner. But just by looking at the website structure one can not infer that