Add link to the parallel module in top-level.
//! - `serde`
//! - Enables serialization support for serde 1.x
//! - `rayon`
-//! - Enables parallel iterators, parallelized methods and [`par_azip!`].
+//! - Enables parallel iterators, parallelized methods, the [`parallel`] module and [`par_azip!`].
//! - Implies std
//! - `approx`
//! - Enables implementations of traits from the [`approx`] crate.
