65f1df594a
Fixed rustc_on_unimplemented example in Unstable Book I saw [this](https://doc.rust-lang.org/beta/unstable-book/language-features/on-unimplemented.html) example and it seemed wrong. This fixes the example to emit an error message that makes more sense.
Rust documentations
Building
To generate all the docs, follow the "Building Documentation" instructions in the README in the root of the repository. This will convert the distributed Markdown docs to HTML and generate HTML doc for the books, 'std' and 'extra' libraries.
To generate HTML documentation from one source file/crate, do something like:
rustdoc --output html-doc/ --output-format html ../src/libstd/path.rs
(This, of course, requires a working build of the rustdoc tool.)
Additional notes
To generate an HTML version of a doc from Markdown manually, you can do something like:
rustdoc reference.md
(reference.md being the Rust Reference Manual.)
An overview of how to use the rustdoc command is available in the docs.
Further details are available from the command line by with rustdoc --help.