message: mention gmp-mpfr-sys only indirectly
diff: @@ -39,10 +39,9 @@ table offers a brief comparison to a few alternatives.
  | Crate | License | Min rustc | Implementation |
  | :--------------- | :------------- | :-------- | :------------- |
  | **`num-bigint`** | MIT/Apache-2.0 | 1.8 | pure rust |
  -| [`gmp-mpfr-sys`] | LGPL-3.0+ | 1.13 | unsafe bindings for [GMP] |
  | [`ramp`] | Apache-2.0 | nightly | rust and inline assembly |
  -| [`rug`] | LGPL-3.0+ | 1.18 | safe interface using `gmp-mpfr-sys` |
  -| [`rust-gmp`] | MIT | stable? | safe bindings for [GMP] |
  +| [`rug`] | LGPL-3.0+ | 1.18 | bundles [GMP] via [`gmp-mpfr-sys`] |
  +| [`rust-gmp`] | MIT | stable? | links to [GMP] |
  [GMP]: https://gmplib.org/
  [`gmp-mpfr-sys`]: https://crates.io/crates/gmp-mpfr-sys
  