README.md in harness-0.2.16 vs README.md in harness-0.3.0

@@ -192,10 +192,19 @@
 ```
 
 ## Rails Integration
 
 Harness will automatically log metrics coming from `ActionPack`,
-`ActiveRecord`, `ActiveSupport` and `ActionMailer`.
+`ActiveRecord`, and `ActionMailer`. `ActiveSupport` instrumentation is
+disabled by default. Also, custom integrations are disabled by default.
+You can turn on instrumentation for specific components like so:
+
+```ruby
+config.harness.instrument.action_controller = false
+config.harness.instrument.active_support = true
+config.harness.instrument.sidekiq = true
+config.harness.instrument.active_model_serializers = true
+```
 
 You can configure Harness from `application.rb`
 
 ```ruby
 config.harness.adapter = :librato