link to article 'How to write documentation' in 'Rust' (#6058)

src/data/roadmaps/rust/content/121-rustdoc.md

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 # Documenting with `rustdoc`
 
 `rustdoc` is a tool that comes bundled with Rust by default. It is primarily used to generate documentation for Rust projects. `rustdoc` takes into consideration both the comments and the source code to produce comprehensive documentation. The resultant documentation can be viewed through a web server or a web browser. The uniqueness of `rustdoc` lies in its testing feature. It can test the code snippets present in your documentation, ensuring that your examples are accurate and up-to-date. It is the de facto tool for all Rust developers to create and maintain their project documentation.
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+Visit the following resources to learn more:
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+- [@article@How to write documentation](https://doc.rust-lang.org/rustdoc/how-to-write-documentation.html)