Add missing description of --symbol-filter in Documentation/perf-report.txt.

Signed-off-by: Namhyung Kim <namhyung.kim@lge.com>
---
 tools/perf/Documentation/perf-report.txt |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/tools/perf/Documentation/perf-report.txt b/tools/perf/Documentation/perf-report.txt
index 87feeee8b90c..68bbf9cec4b7 100644
--- a/tools/perf/Documentation/perf-report.txt
+++ b/tools/perf/Documentation/perf-report.txt
@@ -48,6 +48,9 @@ OPTIONS
 	Only consider these symbols. CSV that understands
 	file://filename entries.
 
+--symbol-filter=::
+	Only show symbols that match (partially) with this filter.
+
 -U::
 --hide-unresolved::
         Only display entries resolved to a symbol.
-- 
1.7.9