Add spring setter

docs/api/animation.md

@@ -11,9 +11,15 @@ Returns a new source with a value always moving torwards the input source value.
         source: () -> T & Animatable,
         period: number = 1,
         damping_ratio: number = 1
-    ): () -> T
+    ): (() -> T, Setter<T>)
 
     type Animatable = number | CFrame | Color3 | UDim | UDim2 | Vector2 | Vector3 | Rect
+
+    type Setter<T> = ({
+        position: T?,
+        velocity: T?,
+        impulse: T?
+    }) -> ()
     ```
 
 - **Details**