Add link to promotion.md (#1033)
Add link to promotion.md (#1033)

* Add link to promotion.md

* Improve link text

Co-authored-by: Camelid <8177b8a8abced623d23d70ce3ff2dc3fbf53888c@gmail.com>

Co-authored-by: Camelid <8177b8a8abced623d23d70ce3ff2dc3fbf53888c@gmail.com>
rust-lang/rustc-dev-guide,rust-lang/rustc-dev-guide,rust-lang/rustc-dev-guide,rust-lang/rustc-dev-guide