More cleanup during review

crates/plugin_runtime/README.md

@@ -39,10 +39,19 @@ Here's an example Rust Wasm plugin that doubles the value of every float in a `V
 ```rust
 use plugin::prelude::*;
 
-#[bind]
+#[export]
 pub fn double(mut x: Vec<f64>) -> Vec<f64> {
     x.into_iter().map(|x| x * 2.0).collect()
 }
 ```
 
-All the serialization code is automatically generated by `#[bind]`.
+All the serialization code is automatically generated by `#[export]`.
+
+You can specify functions that must be defined host-side by using the `#[import]` attribute. This attribute must be attached to a function signature:
+
+```rust
+#[import]
+fn run(command: String) -> Vec<u8>;
+```
+
+The `#[import]` macro will generate a function body that performs the proper serialization/deserialization needed to call out to the host rust runtime. Note that the same ABI is used for both `#[import]` and `#[export]`.