Update deprecation logging doc with logger configuration
Explicitly adds a configuration snippet to change logging level
@@ -194,4 +194,9 @@ logs to roll and compress after 1 GB, and to preserve a maximum of five log
files (four rolled logs, and the active log).
You can disable it in the `config/log4j2.properties` file by setting the deprecation
-log level to `error`.
+log level to `error` like this:
+[source,properties]
+--------------------------------------------------
+logger.deprecation.name = org.elasticsearch.deprecation
+logger.deprecation.level = error
+--------------------------------------------------
