Describe schema when authoring packages using the CLI

refs carvel-dev/kapp-controller#1677

Signed-off-by: Max Brauer <mbrauer@vmware.com>

Author: mamachanko

site/content/kapp-controller/docs/develop/kctrl-package-authoring.md

@@ -118,6 +118,20 @@ certmanager.carvel.dev  certmanager
 Succeeded
 ```
 
+### Reviewing the schema
+
+Once you've got the package put together, it's definitely worth reviewing the details of the package's schema. A package
+communicates its schema as an OpenAPI v3 schema via `.spec.valuesSchema`. The schema gives you the rules for how to put
+together correct values for an installation of the package.
+
+In case of ytt templates, the schema will be exported using [ytt's schema export
+functionality](https://carvel.dev/ytt/docs/latest/how-to-export-schema/).
+
+In case of Helm charts, the schema will be inferred, but this is not a perfect process. The more clearly the Helm chart
+describes its values, the more accurate the schema will be. However, when a field in the Helm chart has `null` as
+its default value, its type cannot be inferred. In that case, it will be assumed to be _any_ possible type. See
+[kapp-controller!1677](https://github.com/carvel-dev/kapp-controller/pull/1677).
+
 ### Relevant FAQs
 - [How can we add additional configuration to an upstream release artifact?](/kapp-controller/docs/latest/kctrl-faq/#how-can-we-add-ytt-overlays-or-additional-configuration-to-upstream-release-artifacts)
 - [How can we go about updating packages dependent on an upstream release?](/kapp-controller/docs/latest/kctrl-faq/#how-can-we-go-about-updating-a-package-dependent-on-an-upstream-release)