perf list: Fix metricgroups title message

$ perf list metricgroups

gives

List of pre-defined events (to be used in -e):

Metric Groups:

Backend
Bad
BadSpec

But that's incorrect of course because metric groups or metrics can only
be specified with -M. So fix the message to say -e or -M

Signed-off-by: Andi Kleen <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/builtin-list.c

···
 	setup_pager();
 
 	if (!raw_dump && pager_in_use())
-		printf("\nList of pre-defined events (to be used in -e):\n\n");
+		printf("\nList of pre-defined events (to be used in -e or -M):\n\n");
 
 	if (hybrid_type) {
 		pmu_name = perf_pmu__hybrid_type_to_pmu(hybrid_type);