feat: add helmfile kcl plugin documents.

docs/user_docs/guides/working-with-k8s/3-mutate-manifests/5-helmfile-kcl-plugin.md

@@ -0,0 +1,94 @@
+---
+title: "Helmfile KCL Plugin"
+sidebar_position: 5
+---
+
+## Introduction
+
+[Helmfile](https://github.com/helmfile/helmfile) is a declarative spec for deploying helm charts. It lets you...
+
++ Keep a directory of chart value files and maintain changes in version control.
++ Apply CI/CD to configuration changes.
++ Periodically sync to avoid skew in environments.
+
+KCL can be used to create functions to mutate and/or validate the YAML Kubernetes Resource Model (KRM) input/output format, and we provide Kustomize KCL functions to simplify the function authoring process.
+
+## Prerequisites
+
++ Install [helmfile](https://github.com/helmfile/helmfile)
++ Prepare a Kubernetes cluster
+
+## Quick Start
+
+Let’s write a KCL function which add annotation `managed-by=helmfile-kcl` only to Deployment resources.
+
+### 1. Get the Example
+
+```bash
+git clone https://github.com/kcl-lang/helmfile-kcl.git
+cd ./helmfile-kcl/examples/hello-world/
+```
+
+We can execute the command to show config
+
+```bash
+cat helmfile.yaml
+```
+
+The output is
+
+```yaml
+repositories:
+- name: prometheus-community
+  url: https://prometheus-community.github.io/helm-charts
+
+releases:
+- name: prom-norbac-ubuntu
+  namespace: prometheus
+  chart: prometheus-community/prometheus
+  set:
+  - name: rbac.create
+    value: false
+  transformers:
+  # Use KCL Plugin to mutate or validate Kubernetes manifests.
+  - apiVersion: krm.kcl.dev/v1alpha1
+    kind: KCLRun
+    metadata:
+      name: "set-annotation"
+      annotations:
+        config.kubernetes.io/function: |
+          container:
+            image: docker.io/kcllang/kustomize-kcl:v0.2.0
+    spec:
+      source: |
+        [resource | {if resource.kind == "Deployment": metadata.annotations: {"managed-by" = "helmfile-kcl"}} for resource in option("resource_list").items]
+```
+
+In the above config, we use a `KCLRun` plugin to assign the `transfomer` field. This means that we will add annotations to all deployment resources in the prometheus helm chart.
+
+### 2. Test and Run
+
+```bash
+helmfile apply
+```
+
+The output is
+
+```bash
+Adding repo prometheus-community https://prometheus-community.github.io/helm-charts
+"prometheus-community" has been added to your repositories
+
+...
+```
+
+## Guides for Developing KCL
+
+Here's what you can do in the KCL code:
+
++ Read resources from `option("resource_list")`. The `option("resource_list")` complies with the [KRM Functions Specification](https://kpt.dev/book/05-developing-functions/01-functions-specification). You can read the input resources from `option("resource_list")["items"]` and the `functionConfig` from `option("resource_list")["functionConfig"]`.
++ Return a KPM list for output resources.
++ Return an error using `assert {condition}, {error_message}`.
+
+## More Documents and Examples
+
++ [Kustomize KCL Plugin](https://github.com/kcl-lang/kustomize-kcl)