Reference helm install docs rather than duplicating (#3418)

* Reference helm install docs rather than duplicating

Multicluster gateway installation docs were out of sync from install docs. This changes them to just directly reference the main install docs to make things more clear.

* Fix syntax

content/docs/setup/kubernetes/multicluster-install/gateways/index.md

@@ -50,22 +50,6 @@ on **each** Kubernetes cluster.
     by a common root CA.
     {{< /tip >}}
 
-1. Generate a multicluster-gateways Istio configuration file using `helm`:
-
-    {{< warning >}}
-    If you're not sure if your `helm` dependencies are up to date, update them using the
-    command shown in [Helm installation steps](/docs/setup/kubernetes/helm-install/#installation-steps)
-    before running the following command.
-    {{< /warning >}}
-
-    {{< text bash >}}
-    $ helm template install/kubernetes/helm/istio --name istio --namespace istio-system \
-        -f @install/kubernetes/helm/istio/values-istio-multicluster-gateways.yaml@ > $HOME/istio.yaml
-    {{< /text >}}
-
-    For further details and customization options, refer to the
-    [Installation with Helm](/docs/setup/kubernetes/helm-install/) instructions.
-
 1. Run the following commands in **every cluster** to deploy an identical Istio control plane
    configuration in all of them.
 
@@ -80,16 +64,10 @@ on **each** Kubernetes cluster.
             --from-file=@samples/certs/cert-chain.pem@
         {{< /text >}}
 
-    * Install Istio's CRDs and wait a few seconds for them to be committed to the Kubernetes API server:
+    * Follow the [Helm Installation Steps](/docs/setup/kubernetes/helm-install/#installation-steps) to install Istio. You must pass in the flag `--values install/kubernetes/helm/istio/values-istio-multicluster-gateways.yaml` to helm to use the correct multicluster settings. For example, using the Helm Install option:
 
         {{< text bash >}}
-        $ for i in install/kubernetes/helm/istio-init/files/crd*yaml; do kubectl apply -f $i; done
-        {{< /text >}}
-
-    * Deploy the Istio control plane:
-
-        {{< text bash >}}
-        $ kubectl apply -f $HOME/istio.yaml
+        $ helm install istio --name istio --namespace istio-system --values install/kubernetes/helm/istio/values-istio-multicluster-gateways.yaml
         {{< /text >}}
 
 ## Setup DNS