docs(changelog): add changelog entry for Nullable additions

Author: glennsl

CHANGELOG.md

@@ -9,11 +9,12 @@
 - Change `Iterator` bindings to have the same shape as `AsyncIterator` for consistency. https://github.com/rescript-association/rescript-core/pull/34
 - Add `Iterator.toArray` binding for turning an iterator into an array. https://github.com/rescript-association/rescript-core/pull/34
 - Add `Array.at` binding for returning an array item by its index. https://github.com/rescript-association/rescript-core/pull/48
-- Fixed type signatures of `Array.fromArrayLikeWithMap` and `Array.fromIteratorWithMap`. https://github.com/rescript-association/rescript-core/pull/50
+- [ ] Fixed type signatures of `Array.fromArrayLikeWithMap` and `Array.fromIteratorWithMap`. https://github.com/rescript-association/rescript-core/pull/50
 - 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
 - Remove `Date.valueOf` as it returns the same as `Date.getTime`. https://github.com/rescript-association/rescript-core/pull/61
+- Add `getExn`, `getUnsafe`, `getWithDefault`, `map`, `mapWithDefault` and `flatMap` to `Nullable`. https://github.com/rescript-association/rescript-core/pull/67
 
 ### Documentation