Update changelog for v0.2.1 release (#6)

Author: danieljharvey

CHANGELOG.md

@@ -4,6 +4,9 @@ This changelog documents the changes between release versions.
 ## [Unreleased]
 Changes to be included in the next upcoming release
 
+## 0.2.1 - 2025.08.15
+* Use `ndc-sdk-python` package version `v0.40`
+
 ## [0.2.0] - 2025-04-02
 * Upgrade Python 3.12 
 * Use `python:3.12-slim` image tag with non-root user.
@@ -109,4 +112,4 @@ Attempting to fix Makefile
 Attempting to fix Makefile
 
 ## [0.0.22] - 2024-07-15
-Attempting to fix workflow and publish package
+Attempting to fix workflow and publish package