Add a note about overriding default Helm options

Author: joeduffy

README.md

@@ -25,4 +25,9 @@ This component supports all of the configuration options of the [official Helm c
 https://github.com/kubernetes/ingress-nginx/tree/main/charts/ingress-nginx), except that these
 are strongly typed so you will get IDE support and static error checking.
 
+The Helm deployment uses reasonable defaults, including the chart name and repo URL, however,
+if you need to override them, you may do so using the `helmOptions` parameter. Refer to
+[the API docs for the `kubernetes:helm/v3:Release` Pulumi type](
+https://www.pulumi.com/docs/reference/pkg/kubernetes/helm/v3/release/#inputs) for a full set of choices.
+
 For complete details, refer to the Pulumi Package details within the Pulumi Registry.