perf report: Document '--call-graph' better for usage

This patch improves 'perf report -h' output for the
'--call-graph' command line option by enumerating the
different output types.

Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frédéric Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1273332783-4268-1-git-send-email-penberg@cs.helsinki.fi>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

tools/perf/builtin-report.c

@@ -457,7 +457,7 @@ static const struct option options[] = {
 	OPT_BOOLEAN('x', "exclude-other", &symbol_conf.exclude_other,
 		    "Only display entries with parent-match"),
 	OPT_CALLBACK_DEFAULT('g', "call-graph", NULL, "output_type,min_percent",
-		     "Display callchains using output_type and min percent threshold. "
+		     "Display callchains using output_type (graph, flat, fractal, or none) and min percent threshold. "
 		     "Default: fractal,0.5", &parse_callchain_opt, callchain_default_opt),
 	OPT_STRING('d', "dsos", &symbol_conf.dso_list_str, "dso[,dso...]",
 		   "only consider symbols in these dsos"),