Add the export queue to the setup docs

Follow-up of backend!2306 (merged)

content/deployment/setup.md

@@ -95,7 +95,7 @@ services:
   worker:
     container_name: ark-worker
     image: registry.gitlab.teklia.com/arkindex/backend:X.Y.Z
-    command: arkindex rqworker-pool --num-workers 2 -v 1 default high tasks
+    command: arkindex rqworker-pool --num-workers 2 -v 1 default high tasks export
 
     depends_on:
       - db