BQ-DTS: Add quickstart

Add quickstart for BigQuery Data Transfer API.

This sample is intended to appear in the documentation at https://cloud.google.com/bigquery/transfer/docs/reference/libraries

Author: tswast

bigquerydatatransfer/quickstart/composer.json

@@ -0,0 +1,9 @@
+{
+    "require": {
+        "php": ">=5.4",
+        "google/cloud-bigquerydatatransfer": "^0.3.2"
+    },
+    "require-dev": {
+        "phpunit/phpunit": "~4"
+    }
+}