convert/test/fixtures/RAR_ATTRIBUTION.md

RAR fixture attribution

sample.rar is a byte-identical copy of testFiles/FolderTest.rar from the YuJianrong/node-unrar.js repository (MIT-licensed), used there for that project's own extraction tests. Reused here because there is no way to create a .rar fixture from this codebase — the unrar library's license bars any tool (including this project's own converters) from writing the RAR format, so RAR support is extraction-only everywhere, including in test fixtures.