Revert removal of docs for default pools argument

doc/source/admin/scaling.md

@@ -376,8 +376,16 @@ gravity:
 ```
 
 In this example 4 processes will be started in total:
-3 processes will act as job handlers and workflow schedulers, and one process will be dedicated to handling jobs for the 
-`special` tag only. With the `job_conf.xml` configuration above these would be jobs created by the `test1` tool.
+3 processes will act as job handlers and workflow schedulers, and one process will be dedicated to handling jobs for the `special` tag only. With the `job_conf.xml` configuration above these would be jobs created by the `test1` tool.
+You can omit the `pools` argument, this will then default to:
+
+```yaml
+        ...
+        pools:
+          - job-handlers
+          - workflow-schedulers
+        ...
+```
 
 If you omit the `processes` argument this will default to a single process.
 You can further customize the handler names using the `name_template` section,