website: media: Add the graphical installer demo.

* website/apps/media/data.scm (playlists): Add graphical installer video.
* website/static/videos/img/guix-system-install.png: New file.

website/apps/media/data.scm

@@ -29,7 +29,17 @@
 GNU Guix."))
      #:url "https://guix.gnu.org/guix-videos/01-installation-from-script.webm"
      #:poster (guix-url "static/videos/img/installation-from-script.png")
-     #:last-updated (string->date "2020-03-28T16:00:00" "~Y-~m-~dT~H:~M:~S")))
+     #:last-updated (string->date "2020-03-28T16:00:00" "~Y-~m-~dT~H:~M:~S"))
+    (video
+     #:title (C_ "video title"
+                 "Demonstration of the Guix System graphical installer")
+     #:page-subpath "system-graphical-installer"
+     #:description
+     (G_ '(p "Walks you through the graphical installer of GNU Guix System."))
+     #:url "https://guix.gnu.org/guix-videos/guix-system-install-1.1.0.webm"
+     #:poster (guix-url "static/videos/img/guix-system-install.png")
+     #:last-updated (string->date "2020-04-15T16:00:00" "~Y-~m-~dT~H:~M:~S")))
+
    (list
     (video
      #:title (C_ "video title" "Everyday use of GNU Guix, Part One")