Clarify the option section header in 'repo help grep'

Signed-off-by: Shawn O. Pearce <sop@google.com>
diff --git a/subcmds/grep.py b/subcmds/grep.py
index 43f5e96..950cc15 100644
--- a/subcmds/grep.py
+++ b/subcmds/grep.py
@@ -33,8 +33,8 @@
   helpDescription = """
 Search for the specified patterns in all project files.
 
-Options
--------
+Boolean Options
+---------------
 
 The following options can appear as often as necessary to express
 the pattern to locate: