Rename the new category to User Experience. Add descriptions.

src/api/03-additional-features/index.md

@@ -1,6 +0,0 @@
----
-name: Additional Features
-slug: additional-features
----
-
-Enhance the basic HTML Video element (`<video>`) with additional features.

src/api/03-user-experience/07-autoplay.md

@@ -1,7 +1,7 @@
 ---
 title: Autoplay
 description: |
-  Make your videos start playback automatically.
+  Learn how to start video playback automatically and employ autoplay strategies that don't lead to degraded user experience.
 date: Septembed 22nd, 2021
 length: '1:04'
 video-sources:

src/api/03-user-experience/index.md

@@ -0,0 +1,6 @@
+---
+name: User Experience
+slug: user-experience
+---
+
+Unleash your videos and learn how autoplay, picture-in-picture and casting can be implemented in ways that improve user experience.