update changelog for donation blurb

CHANGELOG.md

@@ -6,3 +6,10 @@ content of "Unreleased" section content will generate release notes for the
 release.
 
 ## Unreleased
+
+* The initial code base is donated from a
+  [fork](https://github.com/julianocosta89/opentelemetry-microservices-demo) of
+  the [Google microservices
+  demo](https://github.com/GoogleCloudPlatform/microservices-demo) with express
+  knowledge of the owners. The pre-existing copyrights will remain. Any
+  future significant modifications will be credited to OpenTelemetry Authors.