perf_counter tools: add 'perf help'

Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/Documentation/perf_counter/builtin.h b/Documentation/perf_counter/builtin.h
index aec5ae3..800f86c 100644
--- a/Documentation/perf_counter/builtin.h
+++ b/Documentation/perf_counter/builtin.h
@@ -14,6 +14,7 @@
 extern int read_line_with_nul(char *buf, int size, FILE *file);
 extern int check_pager_config(const char *cmd);
 
+extern int cmd_help(int argc, const char **argv, const char *prefix);
 extern int cmd_record(int argc, const char **argv, const char *prefix);
 extern int cmd_stat(int argc, const char **argv, const char *prefix);
 extern int cmd_top(int argc, const char **argv, const char *prefix);