Add a build status badge to README.md

Author: SurferJeffAtGoogle

README.md

@@ -2,6 +2,8 @@
 
 A collection of samples that demonstrate how to call Google Cloud services from PHP.
 
+[![Build Status](https://travis-ci.org/GoogleCloudPlatform/php-docs-samples.svg)](https://travis-ci.org/GoogleCloudPlatform/php-docs-samples)
+
 See our other [Google Cloud Platform github
 repos](https://github.com/GoogleCloudPlatform) for sample applications and
 scaffolding for other frameworks and use cases.