update changelog

Author: RobinMalfait

CHANGELOG.md

@@ -15,6 +15,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - _Upgrade (experimental)_: Install `@tailwindcss/postcss` next to `tailwindcss` ([#14830](https://github.com/tailwindlabs/tailwindcss/pull/14830))
 - _Upgrade (experimental)_: Remove whitespace around `,` separator when print arbitrary values ([#14838](https://github.com/tailwindlabs/tailwindcss/pull/14838))
 
+### Added
+
+- _Upgrade (experimental)_: Migrate `grid-cols-[subgrid]` and `grid-rows-[subgrid]` to `grid-cols-subgrid` and `grid-rows-subgrid` ([#14840](https://github.com/tailwindlabs/tailwindcss/pull/14840))
+
 ## [4.0.0-alpha.31] - 2024-10-29
 
 ### Added