Better explain what the example crate does, and link to doc.rs.

Author: kraktus

src/testing/dev_dependencies.md

@@ -5,7 +5,7 @@ or benchmarks) only. Such dependencies are added to `Cargo.toml` in the
 `[dev-dependencies]` section. These dependencies are not propagated to other
 packages which depend on this package.
 
-One such example is using a crate that extends standard `assert!` macros.  
+One such example is [`pretty_assertions`](https://docs.rs/pretty_assertions/1.0.0/pretty_assertions/index.html), which extends standard `assert_eq!` and `assert_ne!` macros, to provide colorful diff.  
 File `Cargo.toml`:
 
 ```toml