Updating README to reflect --db-data choice.

README.md

@@ -127,10 +127,16 @@ Note! You cannot pass an IP address to the hostname parameter! You need a DNS re
 
 ### Where Are My Files Stored?
 
-When using Docker, all processing results are stored in a docker volume and are not available on the host filesystem. If you want to store your files on the host filesystem instead of a docker volume, you need to pass a path via the `--media-dir` option:
+When using Docker, all processing results are stored in a docker volume and are not available on the host filesystem. There are two specific docker volumes of interest:
+1. Media (called webodm_appmedia): This is where all files related to a project and task are stored.
+2. Postgres DB (called webodm_dbdata): This is what Postgres database uses to store its data.
+
+For more information on how these two volumes are used and in which containers, and in which containers, please refer to the [docker-compose.yml](docker-compose.yml) file. 
+
+For various reasons such as ease of backup/restore, if you want to store your files on the host filesystem instead of a docker volume, you need to pass a path via the `--media-dir` and/or the `--db-dir` options:
 
 ```bash
-./webodm.sh restart --media-dir /home/user/webodm_data
+./webodm.sh restart --media-dir /home/user/webodm_data --db-dir /home/user/webodm_db
 ```
 
 Note that existing task results will not be available after the change. Refer to the [Migrate Data Volumes](https://docs.docker.com/engine/tutorials/dockervolumes/#backup-restore-or-migrate-data-volumes) section of the Docker documentation for information on migrating existing task results.