Update test README.md (#966)

Add flags and its explaination.

test/README.md

@@ -121,6 +121,10 @@ Tests importing [`knative.dev/pkg/test`](#test-library) recognize these flags:
 - [`--cluster`](#specifying-cluster)
 - [`--namespace`](#specifying-namespace)
 - [`--logverbose`](#output-verbose-logs)
+- [`--ingressendpoint`](#specifying-ingress-endpoint)
+- [`--dockerrepo`](#specifying-docker-repo)
+- [`--tag`](#specifying-tag)
+- [`--imagetemplate`](#specifying-image-template)
 
 ### Specifying kubeconfig
 
@@ -178,6 +182,30 @@ The `--logverbose` argument lets you see verbose test logs and k8s logs.
 go test ./test --logverbose
 ```
 
+### Specifying docker repo
+
+The `--dockerrepo` argument lets you specify a uri of the docker repo where you have
+uploaded the test image to using `uploadtestimage.sh`. Defaults to `$KO_DOCKER_REPO`
+
+```bash
+go test ./test --dockerrepo myspecialdockerrepo
+```
+
+### Specifying tag
+
+The `--tag` argument lets you specify the version tag for the test images.
+```bash
+go test ./test --tag v1.0
+```
+
+### Specifying image template
+
+The `--imagetemplate` argument lets you specify a template to generate the
+reference to an image from the test. Defaults to `{{.Repository}}/{{.Name}}:{{.Tag}}`
+```bash
+go test ./test --imagetemplate {{.Repository}}/{{.Name}}:{{.Tag}}
+```
+
 ---
 
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