Update help output to clarify behavior

Signed-off-by: Matt Lord <[email protected]>

go/vt/vtctl/vtctl.go

@@ -2340,7 +2340,7 @@ func commandVRWorkflow(ctx context.Context, wr *wrangler.Wrangler, subFlags *fla
 	const defaultMaxReplicationLagAllowed = defaultWaitTime
 
 	cells := subFlags.String("cells", "", "Cell(s) or CellAlias(es) (comma-separated) to replicate from.")
-	tabletTypes := subFlags.String("tablet_types", "in_order:REPLICA,PRIMARY", "Source tablet types to replicate from (e.g. PRIMARY, REPLICA, RDONLY). Defaults to --vreplication_tablet_type parameter value for the tablet, which has the default value of in_order:REPLICA,PRIMARY.")
+	tabletTypes := subFlags.String("tablet_types", "in_order:REPLICA,PRIMARY", "Source tablet types to replicate from (e.g. PRIMARY, REPLICA, RDONLY). Defaults to --vreplication_tablet_type parameter value for the tablet, which has the default value of in_order:REPLICA,PRIMARY. Note: SwitchTraffic overrides this default and uses in_order:RDONLY,REPLICA,PRIMARY to switch all traffic by default.")
 	dryRun := subFlags.Bool("dry_run", false, "Does a dry run of SwitchReads and only reports the actions to be taken. --dry_run is only supported for SwitchTraffic, ReverseTraffic and Complete.")
 	timeout := subFlags.Duration("timeout", defaultWaitTime, "Specifies the maximum time to wait, in seconds, for vreplication to catch up on primary migrations. The migration will be cancelled on a timeout. --timeout is only supported for SwitchTraffic and ReverseTraffic.")
 	reverseReplication := subFlags.Bool("reverse_replication", true, "Also reverse the replication (default true). --reverse_replication is only supported for SwitchTraffic.")