Adding more clarification in release notes

Author: aliabbasrizvi

CHANGELOG.md

@@ -8,12 +8,14 @@ May 6th, 2019
     - Variation assignments for users activated in an experiment.
     - Feature access for users.
     - Feature variable value for users.
+- Added APIs to be able to conveniently add Decision notification handler (`addDecisionNotificationHandler`) and Track notification handler (`addTrackNotificationHandler`).
 
 ### Bug Fixes:
 - Feature variable APIs return default variable value when featureEnabled property is false. ([#274](https://github.com/optimizely/java-sdk/pull/274))
 
 ### Deprecated
 - Activate notification listener is deprecated as of this release. Recommendation is to use the new Decision notification listener. Activate notification listener will be removed in the next major release.
+- `addActivateNotificationListener`, `addTrackNotificationListener` and `addNotificationListener` APIs on `NotificationCenter`.
 
 ## 3.0.1