docs(argocd-notifications): Use helm-docs (#1015)

* docs(argocd-notifications): Use helm-docs

Signed-off-by: Marco Kilchhofer <mkilchhofer@users.noreply.github.com>

* Use chart appVersion as default image tag

Signed-off-by: Marco Kilchhofer <mkilchhofer@users.noreply.github.com>

charts/argocd-notifications/Chart.yaml

@@ -1,9 +1,9 @@
 apiVersion: v2
-appVersion: 1.1.1
+appVersion: v1.1.1
 description: A Helm chart for ArgoCD notifications, an add-on to ArgoCD.
 name: argocd-notifications
 type: application
-version: 1.5.1
+version: 1.5.2
 home: https://github.com/argoproj/argo-helm
 icon: https://argocd-notifications.readthedocs.io/en/stable/assets/logo.png
 keywords:
@@ -15,4 +15,4 @@ maintainers:
   - name: andyfeller
 annotations:
   artifacthub.io/changes: |
-    - "[Added]: Support annotations on secret objects"
+    - "[Changed]: Use helm-docs to generate README.md"