Document AnnotationsTransformer (#5247)

* Restructure existing Reference docs

Restructure Reference section for site to better match k8s.io. Change
descriptions to complete sentences. Improve instructions to locally load
site.

* Document AnnotationsTransformer on site

Dcoument AnnotationsTransformer API under Reference on site.

* Document required fields

Document required fields and explain effects of optional ones.

* Make site setup instructions more explicit

* Link required K8s fields

site/content/en/docs/Reference/API/Transformers/AnnotationsTransformer.md

@@ -0,0 +1,29 @@
+---
+title: "AnnotationsTransformer"
+linkTitle: "AnnotationsTransformer"
+weight: 1
+date: 2023-07-28
+description: >
+  AnnotationsTransformer adds annotations to user-input resources.
+---
+
+See [Transformers]({{< relref "../Transformers" >}}) for common required fields.
+
+* **apiVersion**: builtin
+* **kind**: AnnotationsTransformer
+* **metadata** ([ObjectMeta](https://kubernetes.io/docs/reference/kubernetes-api/common-definitions/object-meta/#ObjectMeta))
+
+  Standard object's metadata.
+
+* **annotations** (map[string]string)
+
+  Map of annotations that AnnotationsTransformer will add to resources.
+
+  If not specified, AnnotationsTransformer leaves the resources unchanged.
+
+* **fieldSpecs** (\[\][FieldSpec]({{< relref "../Common%20Definitions/FieldSpec.md" >}}))
+
+  fieldSpecs specifies the field on each resource that AnnotationsTransformer should add the annotations to.
+  It essentially allows the user to re-define the field path of the Kubernetes annotations field from `metadata/annotations` for different resources.
+
+  If not specified, AnnotationsTransformer applies the annotations to the `metadata/annotations` field of all resources.

site/content/en/docs/Reference/API/Transformers/_index.md

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+---
+title: "Transformers"
+linkTitle: "Transformers"
+weight: 3
+date: 2023-07-28
+description: >
+  Transformers have the ability to modify user-input resources.
+---
+
+Transformers are Kubernetes objects that dictate how Kustomize changes other Kubernetes objects that users provide.
+Besides `spec`, transformers require the same [fields](https://kubernetes.io/docs/concepts/overview/working-with-objects/#required-fields), listed below, as other Kubernetes objects:
+
+* `apiVersion`
+* `kind`
+* `metadata`
+  * `name`