docs: update description of parameters in storage_upload_file (GoogleCloudPlatform#5707)

* following Java's example https://github.com/googleapis/google-cloud-java/blob/b36db6a957bcfb7b6ccdb77fb12b4cc7fa22b807/google-cloud-examples/src/main/java/com/google/cloud/examples/storage/objects/UploadObject.java#L33-L40

Author: BenWhitehead

storage/cloud-client/storage_upload_file.py

@@ -22,8 +22,11 @@
 
 def upload_blob(bucket_name, source_file_name, destination_blob_name):
     """Uploads a file to the bucket."""
+    # The ID of your GCS bucket
     # bucket_name = "your-bucket-name"
+    # The path to your file to upload
     # source_file_name = "local/path/to/file"
+    # The ID of your GCS object
     # destination_blob_name = "storage-object-name"
 
     storage_client = storage.Client()