Add link to GA4GH presentation to the README file.

This provides a good overview of BigQuery and how it can be used with VT.

Author: arostamianfar

README.md

@@ -15,6 +15,11 @@ It can be used to directly load VCF files to
 [BigQuery](https://cloud.google.com/bigquery/) supporting hundreds of thousands
 of files, millions of samples, and billions of records.
 
+Please see
+[this presentation](https://docs.google.com/presentation/d/1mIjtfAPlojEBa30fZAcene7GRPr9LYo3GRgtQIQMbRY)
+for a high level overview of BigQuery and how to effectively use Variant
+Transforms and BigQuery.
+
 ### Prerequisites
 
 1. Setup a [Google Cloud account](https://cloud.google.com/) and