Create Guide: How to convert Helm templates to ytt templates

## Why
Helm is a common templating tool used in k8s. Often authors that want to use ytt already have helm templates. This guide would provide them with a high level resource to aid in mapping Helm concepts to ytt concepts and features.

## What
This guide would translate Helm concepts (values, templates, --set, template directive) into ytt concepts, and point to the appropriate docs in ytt. This guide would not necessarily compare the two tools or recommend one over the other. It also need not be exhaustive, just touch on concepts that will address the most common use cases.

Here are some Helm concepts that could be touched on:
- values
- `--set` flag
- the template directive
- ...

## How
In a page the carvel.dev/ytt documentation

Here are some requests for this we have gotten [1](https://kubernetes.slack.com/archives/CH8KCCKA5/p1649291738924899?thread_ts=1648229550.805699&cid=CH8KCCKA5) [2](https://github.com/vmware-tanzu/carvel-ytt/issues/130)

Start with the carvel.dev/ytt documentation and review the Helm concepts listed in the issue: values, --set, and the template directive. Create a documentation page that maps those common use cases to ytt concepts and links to the relevant ytt docs; done means the guide is useful without attempting an exhaustive comparison or recommendation.

Written by the indexing model from the issue text.