docs: Add changelog entry for spm4Kmp auto-install

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: buenaflor

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## Unreleased
 
+### Features
+
+- Auto-install Sentry Cocoa for Apple targets when the spm4Kmp plugin (`io.github.frankois944.spmForKmp`) is applied ([#559](https://github.com/getsentry/sentry-kotlin-multiplatform/pull/559))
+
 ### Dependencies
 
 - Bump Kotlin from `2.1.21` to `2.2.21` and Gradle from `8.6` to `8.13` ([#556](https://github.com/getsentry/sentry-kotlin-multiplatform/pull/556))