docs: add CONTRIBUTING.md as a best-practices reference for contributors #214

Job	Run time
Build and test on macOS (macos-latest)	1m 3s
Build and test on Windows (windows-latest)	3m 6s
Build and test makefile	53s
Build and test on Windows (windows-11-arm)	3m 31s
Build and test Fedora on multiple runners (ubuntu-latest)	54s
Build and test Fedora on multiple runners (ubuntu-24.04-arm)	55s
Build and test on macOS (macos-26-intel)	2m 5s
version-release	0s
	12m 27s

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