Updates README about running integration test (#14)

Signed-off-by: Takeshi Yoneda <[email protected]>

Author: mathetake

README.md

@@ -56,6 +56,18 @@ Then execute, for example, the following command to test the passthrough and acc
 curl localhost:1062/uuid
 ```
 
+### Run integration tests with the built example Envoy + Rust Dynamic Module Docker Image.
+
+The integration tests are in the `integration` directory. Assuming you built the Docker image with the tag `envoy-with-dynamic-modules:latest`, you can run the integration tests with the following command:
+```
+cd integration
+go test . -v -count=1
+```
+
+If you want to explicitly specify the docker image, use `ENVOY_IMAGE` environment variable:
+```
+ENVOY_IMAGE=foo-bar-image:latest go test . -v -count=1
+```
 
 ## Update Envoy Version