Add changelog entry

Author: MrAlias

CHANGELOG.md

@@ -28,6 +28,8 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 - `go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc` now keeps the metadata already present in the context when `WithHeaders` is used. (#5892)
 - `go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploggrpc` now keeps the metadata already present in the context when `WithHeaders` is used. (#5911)
 - `go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc` now keeps the metadata already present in the context when `WithHeaders` is used. (#5915)
+- The default global API now supports full auto-instrumentation from the `go.opentelemetry.io/auto` package.
+  See that package for more information. (#5920)
 
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