Add sigma-delta modulation driver to changelog

Issue esp-rs#2370

Author: katyo

esp-hal/CHANGELOG.md

@@ -14,6 +14,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Add burst transfer support to DMA buffers (#2336)
 - `AnyPin` now implements `From<GpioPin<N>>`. (#2326)
 - `Pins::steal()` to unsafely obtain GPIO. (#2335)
+- Added `esp_hal::sdm` Sigma-Delta modulation driver (#2370)
 
 ### Changed