Update CHANGES.md

Author: Doug Black

CHANGES.md

@@ -5,6 +5,13 @@ Here you can see the full list of changes between each twilio-python release.
 
 [2017-07-27] Version 6.5.0
 ---------------------------
+This release adds Beta and Preview products to main artifact.
+
+Previously, Beta and Preview products were only included in the `alpha`
+artifact. They are now being included in the main artifact to ease product
+discoverability and the collective operational overhead of maintaining multiple
+artifacts per library.
+
 **Api**
 - Remove unused `encryption_type` property on Recordings *(breaking change)*
 - Update `status` enum for Messages to include 'accepted'