add documentation for running knative on IBM s390x/IBM ppc64le platforms

docs/install/yaml-install/serving/install-serving-with-yaml-on-IBM-Z-and-IBM-P.md

@@ -0,0 +1,12 @@
+# Install a networking layer on IBM Z and IBM Power platforms
+
+  Patch the deployment **deploy/3-scale-kourier gateway in kourier-system namespace** with latest available image from [redhat catalog](https://catalog.redhat.com/software/containers/openshift-service-mesh/proxyv2-rhel8/5d2cda455a134672890f640a). Check the latest tag and click on the get this image tag to copy the image name. 
+
+  ```bash
+    kubectl patch deployment 3scale-kourier-gateway -n kourier-system -p \
+    '{"spec":{"template":{"spec":{"containers":[{"name":"kourier-gateway" "image":"<replace the proxyv2 image here>"}]}}}}'
+  ```
+
+!!! note
+    1. If there are authentication issues, create [redhat developer account](developers.redhat.com/register) to pull images from redhat catalog. 
+    2. Please refer to the page to [configure pull secrets](https://kubernetes.io/docs/tasks/configure-pod-container/configure-service-account/#add-imagepullsecrets-to-a-service-account)

docs/install/yaml-install/serving/install-serving-with-yaml.md

@@ -29,6 +29,10 @@ To install the Knative Serving component:
 The following tabs expand to show instructions for installing a networking layer.
 Follow the procedure for the networking layer of your choice:
 
+!!! note
+    **Only Kourier network plugin supported for IBM Z and IBM Power platform.** 
+    Follow the below steps to install kourier. Post installation, [Use this alternative documentation](./install-serving-with-yaml-on-IBM-Z-and-IBM-P.md) to patch envoy image since we do not have envoy image support on IBM Z and IBM Power platforms, we will patch the envoy image based on RedHat Maistra.
+
 <!-- TODO: Link to document/diagram describing what is a networking layer.  -->
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