docs: add type_overrides feature to CHANGES.md

Author: enzomaruffa

CHANGES.md

@@ -71,6 +71,7 @@
 
 * (Python) Added exception chaining to preserve error context in CloudSQLEnrichmentHandler, processes utilities, and core transforms ([#37422](https://github.com/apache/beam/issues/37422)).
 * (Python) Added `take(n)` convenience for PCollection: `beam.take(n)` and `pcoll.take(n)` to get the first N elements deterministically without Top.Of + FlatMap ([#X](https://github.com/apache/beam/issues/37429)).
+* Added `type_overrides` parameter to `WriteToBigQuery` allowing users to specify custom BigQuery to Python type mappings when using Storage Write API (Python) ([#25946](https://github.com/apache/beam/issues/25946)).
 * X feature added (Java/Python) ([#X](https://github.com/apache/beam/issues/X)).
 
 ## Breaking Changes