message: add link from infrastructure page
diff: @@ -113,6 +113,7 @@ The state of tools included with Rust are tracked on the [toolstate
  page](https://rust-lang-nursery.github.io/rust-toolstate/). When each PR is
  merged via CI, the status of each tool is recorded in a JSON file and stored
  in the [toolstate repo](https://github.com/rust-lang-nursery/rust-toolstate).
  +For further information, see the [toolstate system documentation](toolstate.html).
  ## Rustup components history
  