message: Add rustbot.
diff: @@ -48,6 +48,13 @@ pending requests for review on [the FCP dashboard](https://rfcbot.rs/).
  Documentation on rfcbot commands can be found
  [in the rfcbot repository](https://github.com/rust-lang/rfcbot-rs).
  +## rustbot
  +
  +[rustbot](https://github.com/rust-lang/triagebot) is a bot ([bot user
  +account](https://github.com/rustbot)) to assist with managing issues and PRs
  +to allow users to label and assign without GitHub permissions. See [the
  +wiki](https://github.com/rust-lang/triagebot/wiki) for more information.
  +
  ## DXR
  [DXR](https://dxr.mozilla.org/rust/source/) is a cross-referenced source index
  