document

rustup doc

    --alloc              The Rust core allocation and collections library
    --book               The Rust Programming Language book
    --cargo              The Cargo Book
    --core               The Rust Core Library
    --edition-guide      The Rust Edition Guide
    --embedded-book      The Embedded Rust Book
	-h, --help               Prints help information
    --nomicon            The Dark Arts of Advanced and Unsafe Rust Programming
    --path               Only print the path to the documentation
    --proc_macro         A support library for macro authors when defining new macros
    --reference          The Rust Reference
    --rust-by-example    A collection of runnable examples that illustrate various Rust concepts and standard
                         libraries
    --rustc              The compiler for the Rust programming language
    --rustdoc            Generate documentation for Rust projects
    --std                Standard library API documentation
    --test               Support code for rustc's built in unit-test and micro-benchmarking framework
    --unstable-book      The Unstable Book