chore(digitaltwins): update changelog (#11017)

sdk/digitaltwins/digitaltwins/CHANGELOG.md

@@ -1,4 +1,9 @@
 # Release History
 
-## 1.0.0-preview.1 (Unreleased)
-- Initial changes
+## 1.0.0-preview.1 (2020-09-03)
+
+- This release is a preview of our efforts to create a client library that is user friendly and
+  idiomatic to the JavaScript ecosystem. The reasons for most of the changes in this update can be found in the
+  [Azure SDK Design Guidelines for TypeScript](https://azure.github.io/azure-sdk/typescript_introduction.html).
+- Initial release:
+  - Package name `@azure/digitaltwins`.