Provide a textual description of the video on the home page for accessibility + provide title

The video on https://playground.xwiki.org/xwiki/bin/view/Main/WebHome is video-only. For the important information in this video, a media-alternative (for instance a transcript) should be provided, so that blind users can receive the same information.

See https://www.w3.org/TR/WCAG21/#audio-only-and-video-only-prerecorded

4.1.2 Name, Role, Value
The iframe containing the video needs a title.