message: README: fix external example gtest_filter
diff: @@ -176,7 +176,7 @@ make EXTERNAL_DIR=external_example
  To run the external hello world integration test, do:
  ```
  -build/default/integration_tests_runner --gtest_filter="HelloWorld*"
  +build/default/integration_tests_runner --gtest_filter="ExternalExampleHello"
  ```
  ### Unit-tests
  