perf bench numa: Add more comment for -c option

Adding more commentary for -c/--show_convergence option, to explain how
the convergence is defined.

Before:
    -c, --show_convergence
                          show convergence details

Now:
    -c, --show_convergence
                          convergence is reached when each process \
	(all its threads) is running on a single NUMA node.

Suggested--by: Jiri Hladky <jhladky@redhat.com>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Hladky <jhladky@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1488732011-27384-1-git-send-email-jolsa@kernel.org
[ Rephrased a bit based on a IRC conversation with Jiri ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/bench/numa.c

@@ -187,7 +187,8 @@ static const struct option options[] = {
 	OPT_INCR   ('d', "show_details"	, &p0.show_details,	"Show details"),
 	OPT_INCR   ('a', "all"		, &p0.run_all,		"Run all tests in the suite"),
 	OPT_INTEGER('H', "thp"		, &p0.thp,		"MADV_NOHUGEPAGE < 0 < MADV_HUGEPAGE"),
-	OPT_BOOLEAN('c', "show_convergence", &p0.show_convergence, "show convergence details"),
+	OPT_BOOLEAN('c', "show_convergence", &p0.show_convergence, "show convergence details, "
+		    "convergence is reached when each process (all its threads) is running on a single NUMA node."),
 	OPT_BOOLEAN('m', "measure_convergence",	&p0.measure_convergence, "measure convergence latency"),
 	OPT_BOOLEAN('q', "quiet"	, &p0.show_quiet,	"quiet mode"),
 	OPT_BOOLEAN('S', "serialize-startup", &p0.serialize_startup,"serialize thread startup"),