metropolis/cli/metroctl: move takeownership under cluster subcommand tree

This is in preparation for having more cluster-wide commands (same as we
keep 'node' for all node-specific commands).

Change-Id: I3fa5935e1d751261bf82a80cf61e811fa36effc9
Reviewed-on: https://review.monogon.dev/c/monogon/+/3593
Tested-by: Jenkins CI
Reviewed-by: Lorenz Brun <lorenz@monogon.tech>
diff --git a/metropolis/handbook/src/ch02-00-local-demo-cluster.md b/metropolis/handbook/src/ch02-00-local-demo-cluster.md
index 76a26c4..1e64e4b 100644
--- a/metropolis/handbook/src/ch02-00-local-demo-cluster.md
+++ b/metropolis/handbook/src/ch02-00-local-demo-cluster.md
@@ -71,7 +71,7 @@
 
 After the first node is set up and running, you can take ownership of the upcoming cluster:
 ```shell
-metroctl takeownership <bootstrap-node-address>
+metroctl cluster takeownership <bootstrap-node-address>
 ```
 This should result in the following output being displayed:
 ```