RED-64539 - replacing namespace placeholders with the name "demo"

this is to improve clarity of the doc, and be consistent with the "demo" namespace that is used in the examples in the doc

Author: randv1r

README.md

@@ -43,6 +43,8 @@ The "Basic" installation deploys the operator (from the current release) from Do
 This is the fastest way to get up and running with a new Redis Enterprise on Kubernetes.
 
 1. Create a new namespace:
+  > Note:
+For the purpose of this doc, we'll use the name "demo" for our cluster's namespace.
 
     ```bash
     kubectl create namespace demo
@@ -111,16 +113,18 @@ This is the fastest way to get up and running with a new Redis Enterprise on Kub
             NAME            TYPE     DATA   AGE
             admission-tls   Opaque   2      2m43s
        ```
+
+    > **Note:** If you're not using multiple namespaces you may proceed to step 6.
+    
     * Enable the Kubernetes webhook using the generated certificate
 
-         **NOTE**: One must replace REPLACE_WITH_NAMESPACE in the following command with the namespace the REC was installed into.
          * Save the certificate into a local environmental variable
          ```shell script
          CERT=`kubectl get secret admission-tls -o jsonpath='{.data.cert}'`
          ```
          * Create a patch file
          ```shell script
-         sed 's/NAMESPACE_OF_SERVICE_ACCOUNT/REPLACE_WITH_NAMESPACE/g' admission/webhook.yaml | kubectl create -f -
+         sed 's/NAMESPACE_OF_SERVICE_ACCOUNT/demo/g' admission/webhook.yaml | kubectl create -f -
    
          cat > modified-webhook.yaml <<EOF
          webhooks:
@@ -264,12 +268,10 @@ Other custom configurations are referenced in this repository.
    ```
     * Enable the Kubernetes webhook using the generated certificate
    
-         **NOTE**: One must replace REPLACE_WITH_NAMESPACE in the following command with the namespace the REC was installed into.
-   
          ```shell script
          # save cert
          CERT=`kubectl get secret admission-tls -o jsonpath='{.data.cert}'`
-         sed 's/NAMESPACE_OF_SERVICE_ACCOUNT/REPLACE_WITH_NAMESPACE/g' admission/webhook.yaml | kubectl create -f -
+         sed 's/NAMESPACE_OF_SERVICE_ACCOUNT/demo/g' admission/webhook.yaml | kubectl create -f -
    
          # create patch file
          cat > modified-webhook.yaml <<EOF