Update README.md (istio#2239)

Automatic merge from submit-queue.

Update README.md

**What this PR does / why we need it**:

**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes #

**Special notes for your reviewer**:

**Release note**:

```release-note
none
```

tests/e2e/README.md

@@ -54,8 +54,10 @@ gcloud container clusters get-credentials ${CLUSTER_NAME} --zone ${ZONE} --proje
 
 ## Step 3: Create Clusterrolebinding
 ```
-kubectl create clusterrolebinding myname-cluster-admin-binding    --clusterrole=cluster-admin    --user="[email protected]"
+kubectl create clusterrolebinding myname-cluster-admin-binding    --clusterrole=cluster-admin    --user="<user_email>"
 ```
+* user_email should be the one you use to log in gcloud command. You can do `gcloud info` to find out current user info.
+
 
 ## Step 4: Export test script variables