Update CHANGELOG.md

Author: jack-burridge-cfh

CHANGELOG.md

@@ -7,6 +7,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## Unreleased
 
+- Move Protobuf encoding to its own package
+  ([#3169](https://github.com/open-telemetry/opentelemetry-python/pull/3169))
 - Implement LowMemory temporality
   ([#3223](https://github.com/open-telemetry/opentelemetry-python/pull/3223))
 - PeriodicExportingMetricReader will continue if collection times out