Adds Aurelia 2 slotted content video

Adds a video tutorial on mastering slotted content in Aurelia 2.

This tutorial explains how to create reusable components using slotted content.

Author: Vheissu

content/videos.md

@@ -4,6 +4,9 @@ description: "Videos for learning Aurelia"
 url: "/videos/"
 type: "videos"
 videos:
+  - title: "Mastering Slotted Content in Aurelia 2"
+    youtube_id: "iX0guNoSyRM"
+    description: "Learn how to use Slotted Content in Aurelia 2 to create reusable components."
   - title: "Working with AppTasks in Aurelia 2"
     youtube_id: "gR5pdsYh1uU"
     description: "Learn how to use AppTasks and how they differ from other Aurelia lifecycles."