Expanded docker.md documentation

docs/deploy/docker.md

@@ -27,6 +27,7 @@ services:
     volumes:
       - umap_userdata:/srv/umap/uploads
       # FIX the path on the left, below, to your location 
+      # OPTIONAL, you can comment the line below out
       - /home/ubuntu/umap.conf:/etc/umap/umap.conf
     restart: always
     depends_on:
@@ -42,3 +43,5 @@ Note that you’ll have to set a [`SECRET_KEY`](https://docs.djangoproject.com/e
 ```sh
 $ python3 -c 'import secrets; print(secrets.token_hex(100))'
 ```
+
+User accounts can be managed via the Django admin page ({SITE_URL}/admin). The required superuser must be created on the container command line with this command: umap createsuperuser.