update readme

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "mappers"
-version = "0.6.0"
+version = "0.6.1"
 edition = "2021"
 description = "Pure Rust geographical projections library"
 repository = "https://github.com/ScaleWeather/mappers"

README.md

@@ -63,3 +63,21 @@ println!("lon: {}, lat: {}", lon, lat); // lon: 6.8651, lat: 45.83260000001716
 ```
 
 Some projections are mathematically exactly invertible, and technically geographical coordinates projected and inverse projected should be identical. However, in practice limitations of floating-point arithmetics will introduce some errors along the way, as shown in the example above.
+
+## Multithreading
+
+For projecting multiple coordinates at once, the crate provides `_parallel`
+functions that are available in a (default) `multithreading` feature. These functions
+use `rayon` crate to parallelize the projection process. They are provided
+mainly for convenience, as they are not much different than calling
+`.par_iter()` on a slice of coordinates and mapping the projection function over it.
+
+```rust
+let lcc = LambertConformalConic::new(2.0, 0.0, 30.0, 60.0, Ellipsoid::WGS84)?;
+
+// Parallel functions use slices of tuples as input and output
+let geographic_coordinates = vec![(6.8651, 45.8326); 10];
+
+let map_coordinates = lcc.project_parallel(&geographic_coordinates)?;
+let inversed_coordinates = lcc.inverse_project_parallel(&map_coordinates)?;
+```