Document how to test charts that contains a CRD

Hi,

I am trying to test a chart that contains some Istio resources and the `ct install` action will fail. I have two options:
1. install the Istio operator as a step in the CI/CD pipeline on the kind cluster before running the tests
2. declare Istio as a dependency of this chart, but enable that only during execution of tests (the helm chart is meant to be used on a cluster where Istio is already installed)

As I tried to do 1. I wasn't able to retrieve the kubeconfig from the create-kind github action and pass it down:

```yml

- name: Create kind cluster
uses: helm/kind-action@v1.4.0
# if: steps.list-changed.outputs.changed == 'true'

- name: Install Istio
uses: huang195/actions-install-istio@v1.0.0
with:
# kubeconfig: "${{steps.kubeconfig.outputs.config}}"
istio version: '1.6.3'
```

Am I following the right approach? Is the approach of declaring a test dependency the right one? How I should declare also a test CRD (an istio Gateway, for example?)