message: Add Rust Pontoon link.
  Link seemed to miss. Based on discussion in
diff: @@ -53,6 +53,7 @@ PRs against [rust-lang/rust-forge].
  * [Bibliography](bibliography.html). Research papers and other links to projects that influenced Rust. Papers about Rust.
  * [Cross compilation resources](cross-compilation/index.html)
  * [Other Rust Installation Methods](other-installation-methods.html)
  +* [Rust Pontoon](https://pontoon.rust-lang.org/). Translating the Rust website.
  <script src="js/moment.min.js"></script>
  