Add changelog

Author: DylanRussell

instrumentation-genai/opentelemetry-instrumentation-google-genai/CHANGELOG.md

@@ -7,6 +7,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## Unreleased
 
+-Add `gen_ai.usage.cache_read.input_tokens` attribute to capture cached tokens on spans/events when the experimental sem conv flag is set. ([#4313](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/4313))
+
 ## Version 0.7b0 (2026-02-20)
 - Fix bug in how tokens are counted when using the streaming `generateContent` method.  ([#4152](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/4152)).
 - Add `gen_ai.tool.definitions` attribute to `gen_ai.client.inference.operation.details` log event ([#4142](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/4142)).