Link to MDN article on browser pointer events (#908)

I read this not knowing what pointer events were and went down a google rabbit hole that lead me to the css property which properly confused me. Hopefully this will save someone else from the same mistake.

content/blog/2018-05-23-react-v-16-4.md

@@ -22,7 +22,7 @@ The following event types are now available in React DOM:
 - `onPointerOver`
 - `onPointerOut`
 
-Please note that these events will only work in browsers that support the Pointer Events specification. (At the time of this writing, this includes the latest versions of Chrome, Firefox, Edge, and Internet Explorer.) If your application depends on pointer events, we recommend using a third-party pointer events polyfill. We have opted not to include such a polyfill in React DOM, to avoid an increase in bundle size.
+Please note that these events will only work in browsers that support the [Pointer Events](https://developer.mozilla.org/en-US/docs/Web/API/Pointer_events) specification. (At the time of this writing, this includes the latest versions of Chrome, Firefox, Edge, and Internet Explorer.) If your application depends on pointer events, we recommend using a third-party pointer events polyfill. We have opted not to include such a polyfill in React DOM, to avoid an increase in bundle size.
 
 [Check out this example on CodeSandbox.](codesandbox://16-4-release-blog-post/pointer-events-example)