message: add some external links to the root libs doc
  These are tactical links that are likely to be regularly useful to the Libs team
diff: # Libs
  This section documents meta processes by the libs team.
  +## External links
  +
  +| Link | Description |
  +|----------|------ |
  +| [Open Libs RFCs](https://github.com/rust-lang/rfcs/pulls?q=is%3Apr+is%3Aopen+label%3AT-libs) | RFCs that need input from the Libs team. |
  +| [Open Libs PRs](https://github.com/rust-lang/rust/pulls?q=is%3Apr+is%3Aopen+label%3AT-libs) | PRs that need input from the Libs team. |
  +| [Libs crates in `rust-lang`](https://github.com/rust-lang?q=topic%3Arust-library) | `topic:rust-library` | Crates in the `rust-lang` organization that are maintained by the Libs team. Add the `rust-library` topic to a repository in `rust-lang` to include it in this list. |
  