Add docs for selectively enabling feature actors

doc/development/feature_flags/index.md

@@ -364,6 +364,8 @@ Feature.enabled?(:feature_flag, group)
 Feature.enabled?(:feature_flag, user)
 ```
 
+Please see [Feature flag controls](controls.md#process) for more details on working with feature flags.
+
 #### Selectively disable by actor
 
 By default you cannot selectively disable a feature flag by actor.