Update opentelemetry-sdk/CHANGELOG.md

point out that this is for exporter authors only

Co-authored-by: Cijo Thomas <[email protected]>

Author: fraillt

opentelemetry-sdk/CHANGELOG.md

@@ -2,7 +2,7 @@
 
 ## vNext
 
-- *Breaking* `start_time` and `time`, in moved from DataPoints to aggregations (Sum, Gauge, Histogram, ExpoHistogram) see [#2377](https://github.com/open-telemetry/opentelemetry-rust/pull/2377) and [#2411](https://github.com/open-telemetry/opentelemetry-rust/pull/2411).
+- *Breaking(Affects custom metric exporter authors only)* `start_time` and `time` is moved from DataPoints to aggregations (Sum, Gauge, Histogram, ExpoHistogram) see [#2377](https://github.com/open-telemetry/opentelemetry-rust/pull/2377) and [#2411](https://github.com/open-telemetry/opentelemetry-rust/pull/2411), to reduce memory.
 
 - *Breaking* `start_time` is no longer optional for `Sum` aggregation, see [#2367](https://github.com/open-telemetry/opentelemetry-rust/pull/2367), but is still optional for `Gauge` aggregation see [#2389](https://github.com/open-telemetry/opentelemetry-rust/pull/2389).