Update changelog

Author: DZakh

CHANGELOG.md

@@ -22,6 +22,7 @@
 - Fix Pervasive.max using boolean comparison for floats. https://github.com/rescript-lang/rescript/pull/7333
 - Experimental: Support nested/inline record types - records defined inside of other records, without needing explicit separate type definitions. https://github.com/rescript-lang/rescript/pull/7241
 - Add unified exponentiation (`**`) operator for numeric types using ES7 `**`. https://github.com/rescript-lang/rescript-compiler/pull/7153
+- Add built-in support for the JavaScript `in` operator. https://github.com/rescript-lang/rescript/pull/7342
 
 #### :boom: Breaking Change