update README.md

README.md

@@ -2,31 +2,20 @@
 
 Adds quantities and units to rust to allow unit safe computation
 
+**Note**: this crate uses an unstable feature which requires you to add `#![feature(generic_const_exprs)]` and use the nightly compiler
+
 ## Define new quantity
 
-### Base Quantity
+currently only three dimensions are supported: Time, Length, Mass
 
 ```rust
-quantity! {
-    name: Time,
-    base_unit: Second,
-    units: {
-        Second:      1e+0,
-        Millisecond: 1e-3,
-    }
-}
-```
+use measurement::{Quantity, Dimension};
 
-### Derived Quantity
+pub type Time = Quantity<Dimension<1 /* time */, 0 /* length */, 0 /* mass */>>;
+pub type Length = Quantity<Dimension<0, 1, 0>>;
+pub type Mass = Quantity<Dimension<0, 0, 1>>;
+
+pub type Velocity = Quantity<Dimension<-1, 1, 0>>;
+pub type Acceleration = Quantity<Dimension<-2, 1, 0>>;
 
-```rust
-quantity! {
-    name: Velocity,
-    base_unit: MeterPerSecond,
-    units: {
-        MeterPerSecond: 1,
-        KilometerPerHour: 3.6,
-    },
-    derive: Length / Time,
-}
 ```