Update README.md: Rename to CHANGELOG.md

Author: aafulei

README.md

@@ -140,7 +140,7 @@ to view the manual page for more information.
 - [`tests/`](./tests/) — test scripts
 - [`.clang-format`](./.clang-format) — Clang Format configuration
 - [`.gitignore`](./.gitignore) — Git ignore patterns
-- [`Changelog.md`](./Changelog.md) — changelog
+- [`CHANGELOG.md`](./CHANGELOG.md) — changelog
 - [`Doxyfile`](./Doxyfile) — Doxygen configuration file
 - [`DoxygenLayout.xml`](./DoxygenLayout.xml) — Doxygen website layout
 - [`LICENSE`](./LICENSE) — license file