Update readme.

tools/redis_to_postgres/README.md

@@ -6,4 +6,6 @@ Navigate to the `tools/redis_to_postgres` directory and ensure that the environm
 docker compose up --build --abort-on-container-exit
 ```
 
-This will run database schema migrations for Postgres and then copy data from Redis to Postgres. Eventually all containers will be stopped.
+This will run database schema migrations for Postgres and then copy data from Redis to Postgres. Eventually all containers will be stopped.
+
+Note: if you were not using Redis locally and instead were using a remote Redis instance (for example on AWS), you can simply set the `REDIS_URL` environment variable to the remote instance's address, remove the `redis` service from the docker-compose file, and run the same command as above.