docs: restructure docs and add tutorials (#2883)

Co-authored-by: knqyf263 <knqyf263@gmail.com>

docs/tutorials/kubernetes/gitops.md

@@ -0,0 +1,125 @@
+# Installing the Trivy-Operator through GitOps
+
+This tutorial shows you how to install the Trivy Operator through GitOps platforms, namely ArgoCD and FluxCD.
+
+## ArgoCD
+
+Make sure to have [ArgoCD installed](https://argo-cd.readthedocs.io/en/stable/getting_started/) and running in your Kubernetes cluster.
+
+You can either deploy the Trivy Operator through the argocd CLI or by applying a Kubernetes manifest.
+
+ArgoCD command:
+```
+> kubectl create ns trivy-system
+> argocd app create trivy-operator --repo https://github.com/aquasecurity/trivy-operator --path deploy/helm --dest-server https://kubernetes.default.svc --dest-namespace trivy-system
+```
+Note that this installation is directly related to our official Helm Chart. If you want to change any of the value, we'd suggest you to create a separate values.yaml file.
+
+Kubernetes manifest `trivy-operator.yaml`:
+```
+apiVersion: argoproj.io/v1alpha1
+kind: Application
+metadata:
+  name: trivy-operator
+  namespace: argocd
+spec:
+  project: default
+  source:
+    chart: trivy-operator
+    repoURL: https://aquasecurity.github.io/helm-charts/
+    targetRevision: 0.0.3
+    helm:
+      values: |
+        trivy:
+          ignoreUnfixed: true
+  destination:
+    server: https://kubernetes.default.svc
+    namespace: trivy-system
+  syncPolicy:
+    automated:
+      prune: true
+      selfHeal: true
+```
+
+The apply the Kubernetes manifest. If you have the manifest locally, you can use the following command through kubectl:
+```
+> kubectl apply -f trivy-operator.yaml
+
+application.argoproj.io/trivy-operator created
+```
+
+If you have the manifest in a Git repository, you can apply it to your cluster through the following command:
+```
+> kubectl apply -n argocd -f https://raw.githubusercontent.com/AnaisUrlichs/argocd-starboard/main/starboard/argocd-starboard.yaml
+```
+The latter command would allow you to make changes to the YAML manifest that ArgoCD would register automatically.
+
+Once deployed, you want to tell ArgoCD to sync the application from the actual state to the desired state:
+```
+argocd app sync trivy-operator
+```
+
+Now you can see the deployment in the ArgoCD UI. Have a look at the ArgoCD documentation to know how to access the UI.
+
+![ArgoCD UI after deploying the Trivy Operator](../../imgs/argocd-ui.png)
+
+Note that ArgoCD is unable to show the Trivy CRDs as synced.
+
+
+## FluxCD
+
+Make sure to have [FluxCD installed](https://fluxcd.io/docs/installation/#install-the-flux-cli) and running in your Kubernetes cluster.
+
+You can either deploy the Trivy Operator through the Flux CLI or by applying a Kubernetes manifest.
+
+Flux command:
+```
+> kubectl create ns trivy-system
+> flux create source helm trivy-operator --url https://aquasecurity.github.io/helm-charts --namespace trivy-system
+> flux create helmrelease trivy-operator --chart trivy-operator
+  --source HelmRepository/trivy-operator
+  --chart-version 0.0.3
+  --namespace trivy-system
+```
+
+Kubernetes manifest `trivy-operator.yaml`:
+```
+apiVersion: source.toolkit.fluxcd.io/v1beta2
+kind: HelmRepository
+metadata:
+  name: trivy-operator
+  namespace: flux-system
+spec:
+  interval: 60m
+  url: https://aquasecurity.github.io/helm-charts/
+
+---
+apiVersion: helm.toolkit.fluxcd.io/v2beta1
+kind: HelmRelease
+metadata:
+  name: trivy-operator
+  namespace: trivy-system
+spec:
+  chart:
+    spec:
+      chart: trivy-operator
+      sourceRef:
+        kind: HelmRepository
+        name: trivy-operator
+				namespace: flux-system
+      version: 0.0.5
+  interval: 60m
+```
+
+You can then apply the file to your Kubernetes cluster:
+```
+kubectl apply -f trivy-operator.yaml
+```
+
+## After the installation
+
+After the install, you want to check that the Trivy operator is running in the trivy-system namespace:
+```
+kubectl get deployment -n trivy-system
+```
+