message: Update and improve wording of exposing K8s API warning.
diff: - Add custom and private chart repositories (supports [ChartMuseum](https://github.com/helm/chartmuseum) and [JFrog Artifactory](https://www.jfrog.com/confluence/display/RTF/Helm+Chart+Repositories))
  - Browse and provision external services from the [Service Catalog](https://github.com/kubernetes-incubator/service-catalog) and available Service Brokers
  - Connect Helm-based applications to external services with Service Catalog Bindings
  -- Secure authentication and authorization based on Kubernetes [Role-Based Access Control](https://github.com/kubeapps/kubeapps/blob/master/docs/user/access-control.md)
  +- Secure authentication to Kubeapps using an [OAuth2/OIDC provider](https://github.com/kubeapps/kubeapps/blob/master/docs/user/using-an-OIDC-provider.md)
  +- Secure authorization based on Kubernetes [Role-Based Access Control](https://github.com/kubeapps/kubeapps/blob/master/docs/user/access-control.md)
  ## TL;DR;
  @@ -117,7 +118,7 @@ Learn more about how to secure your Kubeapps installation [here](https://github.
  ### Exposing Externally
  -> **Note**: The Kubeapps frontend sets up a proxy to the Kubernetes API service, so when when exposing the Kubeapps service to a network external to the Kubernetes cluster (perhaps on an internal or public network), the Kubernetes API will also be exposed on that network. See [#1111](https://github.com/kubeapps/kubeapps/issues/1111) for more details.
  +> **Note**: The Kubeapps frontend sets up a proxy to the Kubernetes API service which means that when exposing the Kubeapps service to a network external to the Kubernetes cluster (perhaps on an internal or public network), the Kubernetes API will also be exposed for authenticated requests from that network. If you explicitly [use an OAuth2/OIDC provider with Kubeapps](https://github.com/kubeapps/kubeapps/blob/master/docs/user/using-an-OIDC-provider.md) (recommended), then only the configured users trusted by your Identity Provider will be able to reach the Kubernetes API. See [#1111](https://github.com/kubeapps/kubeapps/issues/1111) for more details.
  #### LoadBalancer Service
  