CHANGELOG: add patch for 1221

Author: dannywillems

CHANGELOG.md

@@ -27,6 +27,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - **Development Tools**: Enhanced formatting infrastructure with MDX file
   support and trailing whitespace management
   ([#1234](https://github.com/o1-labs/openmina/pull/1234))
+- **Makefile**: Add `run-block-producer` target with devnet/mainnet support and
+  `generate-block-producer-key` target for key generation
+  ([#1221](https://github.com/o1-labs/openmina/pull/1221)).
 
 ### Changed