docs(instance): add documentation on placement group (#1520)

Author: scaleway-bot

cmd/scw/testdata/test-all-usage-instance-placement-group-update-usage.golden

@@ -18,8 +18,8 @@ EXAMPLES:
 ARGS:
   placement-group-id   UUID of the placement group
   [name]               Name of the placement group
-  [policy-mode]         (optional | enforced)
-  [policy-type]         (max_availability | low_latency)
+  [policy-mode]        The operating mode of the placement group (optional | enforced)
+  [policy-type]        The policy type of the placement group (max_availability | low_latency)
   [zone=fr-par-1]      Zone to target. If none is passed will use default zone from the config (fr-par-1 | fr-par-2 | nl-ams-1 | pl-waw-1)
 
 FLAGS:

internal/namespaces/instance/v1/instance_cli.go

@@ -2088,13 +2088,15 @@ func instancePlacementGroupUpdate() *core.Command {
 			},
 			{
 				Name:       "policy-mode",
+				Short:      `The operating mode of the placement group`,
 				Required:   false,
 				Deprecated: false,
 				Positional: false,
 				EnumValues: []string{"optional", "enforced"},
 			},
 			{
 				Name:       "policy-type",
+				Short:      `The policy type of the placement group`,
 				Required:   false,
 				Deprecated: false,
 				Positional: false,