imagePullSecrets isn't added nor mentioned in any docs

I wasted hours trying to pull from a private repo, despite portainer adding pull secrets for each name space (via the UI) it doesn't actually update nor mention you need to add:
```
      imagePullSecrets:
        - name: registry-1
```

to your deployments, can this at minimum be mentioned in docs or automatically added to the charts when enabling the namespace access to the registries.