Update README

Author: ericgross

Diff for: README.md

@@ -27,6 +27,7 @@ Set your source and target databases, as well as your s3 intermediary.
 ```bash
 export POSTGRES_TO_REDSHIFT_SOURCE_URI='postgres://username:password@host:port/database-name'
 export POSTGRES_TO_REDSHIFT_TARGET_URI='postgres://username:password@host:port/database-name'
+export POSTGRES_TO_REDSHIFT_TARGET_SCHEMA='testing-data'
 export S3_DATABASE_EXPORT_ID='yourid'
 export S3_DATABASE_EXPORT_KEY='yourkey'
 export S3_DATABASE_EXPORT_BUCKET='some-bucket-to-use'