docs: Add CHANGELOG.md for v1.2.0

Author: suyulin

CHANGELOG.md

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+# Changelog
+
+## v1.2.0
+
+This release includes updated Rockchip chip code mappings, bug fixes for firmware packing, and improved documentation.
+
+### Features
+- **Updated Chip Mappings**: The tool now recognizes a more comprehensive list of Rockchip SoCs, ensuring better compatibility and more accurate chip identification during both packing and unpacking. This includes new mappings for `RV1109/RV1126`, `RK3528`, `RK3308`, and many others.
+
+### Bug Fixes
+- **Packing/Unpacking Special Partitions**: Fixed a critical bug where the tool would fail when packing or unpacking firmware containing special partitions like `RESERVED` or `backup`. The tool now correctly handles these partitions, preventing crashes and ensuring that firmware images can be repacked successfully.
+
+### Documentation
+- **Updated READMEs**: Both `README.md` and `README_CN.md` have been updated with the latest list of supported chip families, providing users with up-to-date information on device compatibility.