add guides to docs

possible guides to add:

- building basic config (and doing some reuse)
- data values vs functions
- writing simple k8s app
- should use ytt-k8s-starter
- combining multiple k8s apps together into one configuration
- involves dealing with libraries
- ytt for Helm Templaters
- why would you even do this?
- converting an example
- ways to implement Helm-y features (e.g. releases)

Start by reviewing the proposed topics: basic configuration and reuse, a simple Kubernetes app using ytt-k8s-starter, combining apps with libraries, and using ytt for Helm templating. Define the guide structure and examples for each topic, with completion meaning that the selected guides are written and cover the listed questions and workflows.

Written by the indexing model from the issue text.