Add some usage information

README.md

@@ -1,12 +1,33 @@
-# strongly
+# strongly::typed
 
 [WIP] A proc macro to create strongly-typed primitives.
 
+## Usage
+
+Add the `#[strongly::typed(<primitive>)]` attribute to your unit struct to turn
+it into a strongly-typed primitive. Supports all integers and floats, plus
+`bool` and `char`.
+
+```rust
+#[strongly::typed(u8)]
+pub struct SpecialInt;
+```
+
+The attribute will also add all nine possible default derives (`Copy`, `Clone`,
+`Default`, etc.) and set `#[repr(transparent)]`.
+
+## Features
+
+* Default: `std`
+* `std`: Doesn't do anything at the moment.
+* `serde`: Generate implementations of `Serialize` and `Deserialize` to and from
+  the representation of the primitive.
+
 ## Caveats
 
-* It's not possible to loop over strongly-typed integer ranges
-  because the `Step` trait is unstable. Instead, the macro generates
-  helper methods to create (strongly-typed) iterators.
+* It's not possible to loop over strongly-typed integer ranges because the
+  `Step` trait is unstable. Instead, the macro generates helper methods to
+  create (strongly-typed) iterators.
 * Strongly-typed `bool`s cannot be directly used as `if` condition expressions
   nor can they be directly used in `&&` and `||` operations as these are not
   implementable. (TODO: Offer `Deref<Target=bool>` via feature.)