add missing import (see #174) (#198)

src/view/04b_iteration.md

@@ -353,6 +353,8 @@ On the other hand, it’s the newest API. As of writing this sentence (December
 
 Here’s the complete store example. You can find another, more complete example [here](https://github.com/leptos-rs/leptos/blob/main/examples/stores/src/lib.rs), and more discussion in the book [here](../15_global_state.md).
 ```
+use reactive_stores::Store;
+
 #[derive(Store, Debug, Clone)]
 pub struct Data {
     #[store(key: String = |row| row.key.clone())]