Add Linked Role tutorial video

[CodingKoopa]

We want to show users how to obtain the linked role to speak in chat.

• Evaluate the best format (WEBM? MP4? probably not GIF)
• Record video tutorial on desktop.
• Record video tutorial on mobile. Both iOS and Android use a uniform React Native interface, so it shouldn't matter which it's recorded on.
• Add video tutorial to /profile with a slider toggling between mobile and desktop.
• Make slider default to the detected platform.
• Also add video tutorial to a Discord channel at the very top.

This should be a carefully trimmed video w/o audio that loops nicely.

[CodingKoopa]

Mockup:

where the mobile/desktop thing is a button group