fix writing

README.md

@@ -171,7 +171,9 @@ assert_eq!(format!("{:?}", length / time), "5000 m s^-1")
 # Custom unit systems
 ## The `unit_system` macro
 Diman also provides the `unit_system` macro for defining custom
-unit systems for everything that is not covered by SI alone.
+unit systems for everything that is not covered by SI alone. The
+macro will add a new quantity type and implement all the required
+methods and traits to make it usable.
 As an example, consider the following macro call:
 ```rust
 diman::unit_system!(

src/lib.rs

@@ -210,7 +210,9 @@
 //! # Custom unit systems
 //! ## The `unit_system` macro
 //! Diman also provides the `unit_system` macro for defining custom
-//! unit systems for everything that is not covered by SI alone.
+//! unit systems for everything that is not covered by SI alone. The
+//! macro will add a new quantity type and implement all the required
+//! methods and traits to make it usable.
 //! As an example, consider the following macro call:
 //! ```
 //! # #![allow(incomplete_features)]