Fix outdated Try_ConvertResult documentation

[wenxiaojie1]

Fixes #175.\n\nReplaces the removed Try_ConvertResult derive in the published README and crate-level API example with the current #[FromResidual(Result<_, Self::Residual>)] pattern.\n\nValidation:\n- git diff --check\n- Confirmed no remaining Try_ConvertResult references in README.md or crates/try_v2/src/lib.rs\n\ncargo doc was not run locally because this Windows environment has no Rust toolchain; the repository CI remains the compilation check.

[sourcery-ai]

Hey - I've reviewed your changes and they look great!

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