docs: update changelog

Author: glennsl

CHANGELOG.md

@@ -13,6 +13,7 @@
 - Remove internal async/await helpers that do not need to be exposed in `Core`.
 - Add locale and formatting options to `localeDateString`, `localeString` and `localTimeString` functions https://github.com/rescript-association/rescript-core/pull/30
 - Change `RegExp.source` to return a `string`. Was previously returning a `bool`, which is wrong. https://github.com/rescript-association/rescript-core/pull/47
+- Add `flat`, `expect`, and `or` to `Option`, deprecate `orElse`.
 
 ### Documentation