Add link from "Writing Documentation" suggestion
Add link from "Writing Documentation" suggestion

A link to the relevant section of the contributing documentation makes it easier for contributors to locate the relevant information. (e.g. via an in-page search for "doc".)

This is particularly important currently as https://github.com/rust-lang/rust/blob/85072e330394440776ace5ae612e3ced32ef6348/CONTRIBUTING.md links directly to the (currently `rustc`-focused) "Getting Started" guide rather than the general Rust contribution content to which it used to point.
rust-lang/rustc-dev-guide,rust-lang/rustc-dev-guide,rust-lang/rustc-dev-guide,rust-lang/rustc-dev-guide