README.md in rack-graphql-2.4.0 vs README.md in rack-graphql-2.5.0

@@ -24,10 +24,11 @@
 ```ruby
 run RackGraphql::Application.call(
   schema: YourGraqphqlSchema,                      # required
   app_name: 'your-service-name',                   # optional, used for health endpoint content
   context_handler: YourGraphqlContextHandler,      # optional, empty `proc` by default
-  log_exception_backtrace: !A9n.env.production?,   # optional, `true` default
+  log_exception_backtrace: !A9n.env.production?,   # optional, `false` default
+  # `true` when `RACK_GRAPHQL_LOG_EXCEPTION_BACKTRACE` env var is set to `'1'` or `'true'`
   health_route: true,                              # optional, true by default
   logger: A9n.logger,                              # optional, not set by default
   error_status_code_map: { IamTeapotError => 418 }, # optional
 )
 ```