Add prerequisite to install semistandard (required for npm test) (GoogleCloudPlatform#447)

Author: remi Taylor

README.md

@@ -132,9 +132,14 @@ on Google Cloud Platform.
 
  Read more about [Google Cloud Platform Authentication][gcp_auth].
 
+ __Note for running unit tests:__
+
+ Install [semistandard][] (lint tool)
+
 [node]: https://nodejs.org/
 [auth_command]: https://cloud.google.com/sdk/gcloud/reference/beta/auth/application-default/login
 [gcp_auth]: https://cloud.google.com/docs/authentication#projects_and_resources
+[semistandard]: https://www.npmjs.com/package/semistandard
 
 ### How to run a sample