Dreams really do come true! Don't worry if you don't see the update immediately, as Facebook is still rolling it out. This news comes as quite the surprise as Facebook previously avoided supporting GIFs because they felt it would clutter up the News Feed.
Facebook already built-in GIF support a while back, but instead chose to focus on auto-playing video. Even after Twitter accommodated GIFs last summer, Facebook still stuck to the idea that GIFs weren't a great idea.
To post, all you need to do is use a link hosted on sites like Giphy or Tumblr, and it will animate after you hit publish. Unfortunately, you can't upload a GIF directly just yet, but it *will* auto-play in your timeline just like video.