Add <Activity> bullet to built-in components section

Author: imjordanxd

src/content/reference/react/components.md

@@ -16,6 +16,7 @@ React exposes a few built-in components that you can use in your JSX.
 * [`<Profiler>`](/reference/react/Profiler) lets you measure rendering performance of a React tree programmatically.
 * [`<Suspense>`](/reference/react/Suspense) lets you display a fallback while the child components are loading.
 * [`<StrictMode>`](/reference/react/StrictMode) enables extra development-only checks that help you find bugs early.
+* [`<Activity>`](/reference/react/Activity) lets you hide and restore the UI and internal state of its children.
 
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