Make PR references in CHANGELOG links

Author: adamwathan

CHANGELOG.md

@@ -9,9 +9,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
-- Dark mode variant (experimental) (#2279)
-- New `preserveHtmlElements` option for `purge` (#2283)
-- New `layers` mode for `purge` (#2288)
+- Dark mode variant (experimental) ([#2279](https://github.com/tailwindlabs/tailwindcss/pull/2279))
+- New `preserveHtmlElements` option for `purge` ([#2283](https://github.com/tailwindlabs/tailwindcss/pull/2283))
+- New `layers` mode for `purge` ([#2288](https://github.com/tailwindlabs/tailwindcss/pull/2288))
 
 ### Deprecated