Small update to Animations docs (facebook#4160)

This text appears to be referencing a class component that uses state to store the animated value. The example it is referencing is using function components, and the animated value is not state.

Author: joevilches

docs/animations.md

@@ -130,7 +130,7 @@ export default () => {
 </TabItem>
 </Tabs>
 
-Let's break down what's happening here. In the `FadeInView` constructor, a new `Animated.Value` called `fadeAnim` is initialized as part of `state`. The opacity property on the `View` is mapped to this animated value. Behind the scenes, the numeric value is extracted and used to set opacity.
+Let's break down what's happening here. In the `FadeInView` render method, a new `Animated.Value` called `fadeAnim` is initialized with `useRef`. The opacity property on the `View` is mapped to this animated value. Behind the scenes, the numeric value is extracted and used to set opacity.
 
 When the component mounts, the opacity is set to 0. Then, an easing animation is started on the `fadeAnim` animated value, which will update all of its dependent mappings (in this case, only the opacity) on each frame as the value animates to the final value of 1.