Update CHANGELOG.md - Version 0.3.0

Author: aafulei

CHANGELOG.md

@@ -1,5 +1,39 @@
 # Changelog
 
+## [0.3.0]() - 2025-05-16
+
+**Managing a single source of truth between program and man page.**
+
+### Added
+
+- Source code:
+    - `VERSION` macro
+    - `--help` and `--version` options
+- Build system:
+    - `make man`
+    - `make dist`
+    - `make install/uninstall`
+    - `make show-version`
+- Project website:
+    - User Guide section
+    - Technical Details section
+        - Single Source of Truth subsection
+        - Makefile in Detail subsection
+        - Ready for Deployment subsection
+    - Enable extension for code highlight
+- Manual page:
+    - Man page with conversion from `help2man`
+- Assets:
+    - Mermaid diagrams for project website and code reference
+    - Screenshots of man page and help info
+
+### Changed
+
+- Build system:
+    - Do not use `BINSTAMP`; just use order-only prerequisite on `BIN_DIR`
+- Assets:
+    - Rename `.svg` files; do not use soft links
+
 ## [0.2.0]() - 2025-05-14
 
 **Integrated with Doxygen for source code documentation.**