Fix typo (#42)

signa -> signal

src/reactivity/14_create_effect.md

@@ -80,7 +80,7 @@ create_effect(move |_| {
 let b = move || a() * 2;
 ```
 
-If you need to synchronize some reactive value with the non-reactive world outside—like a web API, the console, the filesystem, or the DOM—writing to a signal in an effect is a fine way to do that. In many cases, though, you’ll find that you’re really writing to a signa inside an event listener or something else, not inside an effect. In these cases, you should check out [`leptos-use`](https://leptos-use.rs/) to see if it already provides a reactive wrapping primitive to do that!
+If you need to synchronize some reactive value with the non-reactive world outside—like a web API, the console, the filesystem, or the DOM—writing to a signal in an effect is a fine way to do that. In many cases, though, you’ll find that you’re really writing to a signal inside an event listener or something else, not inside an effect. In these cases, you should check out [`leptos-use`](https://leptos-use.rs/) to see if it already provides a reactive wrapping primitive to do that!
 
 > If you’re curious for more information about when you should and shouldn’t use `create_effect`, [check out this video](https://www.youtube.com/watch?v=aQOFJQ2JkvQ) for a more in-depth consideration!