Update CHANGELOG.md

Author: cristianoc

CHANGELOG.md

@@ -22,6 +22,7 @@
 - Added infra to modernise AST: theres' Parsetree, Parsetree0 (legacy), and conversion functions to keep compatibility with PPX. https://github.com/rescript-lang/rescript/pull/7185
 - Ast cleanup: remove exp object and exp unreachable. https://github.com/rescript-lang/rescript/pull/7189
 - Ast cleanup: explicit representation for optional record fields in types. https://github.com/rescript-lang/rescript/pull/7190 https://github.com/rescript-lang/rescript/pull/7191
+- AST cleanup: first-class expression and patterns for records with optional fields. https://github.com/rescript-lang/rescript/pull/7192
 
 
 # 12.0.0-alpha.5