doc: update ArgoCD README sections

- Add instructions on how to access ArgoCD dashboard via `argocdm admin dashboard`
- Mention possible requirement to switch namespace to `argocd`

🤖

README.md

@@ -23,6 +23,13 @@ make sure kubectl is configure to reach the destination cluster, then:
 
 ## Notes
 
+### ArgoCD
+
+As the ArgoCD server is not deployed, the dashboard can only be accessed via  
+`argocdm admin dashboard`
+
+(It may be required switch the namespace to `argocd` beforehand)
+
 ### Linode
 
 PROXY protocol needs to be enabled for ingress-nginx to see the clients IP in ingress log.