docs: update changelog

Author: sscovil

typescript/CHANGELOG.md

@@ -4,6 +4,13 @@ All notable changes to the Radius TypeScript SDK will be documented in this file
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+### Added
+- Type exports for `BigNumberish`, `BytesLike`, and `HttpClient`, required for custom `Signer` implementations
+
+### Security
+- Added pnpm override for `esbuild` requiring v0.25.0 or above, to address a known security vulnerability
+
 ## 1.0.0
 ### Added
 - Initial SDK implementation