Improve documentation on JsonFileToFlatbuffer

Change-Id: I19fab5db13f10bc119d28d7b25adb1274759e901
Signed-off-by: Austin Schuh <austin.schuh@bluerivertech.com>
diff --git a/aos/json_to_flatbuffer.h b/aos/json_to_flatbuffer.h
index 7168e4c..45920a8 100644
--- a/aos/json_to_flatbuffer.h
+++ b/aos/json_to_flatbuffer.h
@@ -102,7 +102,8 @@
             std::ostreambuf_iterator<char>(file));
 }
 
-// Parses a file as JSON and returns the corresponding Flatbuffer, or dies.
+// Parses a file as JSON and returns the corresponding Flatbuffer. Dies if
+// reading the file fails, returns an empty buffer if the contents are invalid.
 template <typename T>
 inline FlatbufferDetachedBuffer<T> JsonFileToFlatbuffer(
     const std::string_view path) {