minor update

Signed-off-by: jiajunye <[email protected]>

docs/root/overview.md

@@ -191,7 +191,9 @@ formats. It’s like having the cake and eating it too!
 
 ## User-specified Nighthawk logging
 
-Users can use their own Nighthawk logging options when calling **ENVOY_LOG**.
-Basically it would require two steps:
+Users of Nighthawk can specify custom format and destination (logging sink
+delegate) for all Nighthawk logging messages. Nighthawk utilizes the Envoy's
+logging mechanism by performing all logging via the **ENVOY_LOG** macro. To
+customize this mechanism, users need to perform two steps:
 1. Create a logging sink delegate inherited from [Envoy SinkDelegate](https://github.com/envoyproxy/envoy/blob/master/source/common/common/logger.h).
 2. Constructor a ServiceImpl object with an [Envoy Logger Context](https://github.com/envoyproxy/envoy/blob/master/source/common/common/logger.h) which contains user-specified log level and format.