Update create-product.js

Author: rebeccaellis

retail/interactive-tutorials/product/create-product.js

@@ -11,6 +11,7 @@
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
+// [START retail_create_product]
 
 'use strict';
 
@@ -77,3 +78,4 @@ process.on('unhandledRejection', err => {
 });
 
 main(...process.argv.slice(2));
+// [END retail_create_product]