docs: clarify difference between set() and update()

docs/book/src/view/01_basic_component.md

@@ -90,7 +90,8 @@ view! { cx,
     <button
         // define an event listener with on:
         on:click=move |_| {
-            set_count.update(|n| *n += 1);
+            // on stable, this is set_count.set(3);
+            set_count(3);
         }
     >
         // text nodes are wrapped in quotation marks
@@ -142,6 +143,16 @@ in a function, telling the framework to update the view every time `count` chang
 `{count()}` access the value of `count` once, and passes an `i32` into the view,
 rendering it once, unreactively. You can see the difference in the CodeSandbox below!
 
+Let’s make one final change. `set_count(3)` is a pretty useless thing for a click handler to do. Let’s replacing “set this value to 3” with “increment this value by 1”:
+
+```rust
+move |_| {
+    set_count.update(|n| *n += 1);
+}
+```
+
+You can see here that while `set_count` just sets the value, `set_count.update()` gives us a mutable reference and mutates the value in place. Either one will trigger a reactive update in our UI.
+
 > Throughout this tutorial, we’ll use CodeSandbox to show interactive examples. To
 > show the browser in the sandbox, you may need to click `Add DevTools >
 Other Previews > 8080.` Hover over any of the variables to show Rust-Analyzer details