Add a website badge and a walkthrough video to the README

[amaudruz]

Two commits.

CHOO-2351

Website badge. Links to https://www.flintai.dev/products/switch, first in the row and ahead of the license. Everything else there — license, docs, contributing, Discord — assumes you have already decided to use Switch; someone who has just landed and wants to know what it is had nowhere to go.

Watch it work, immediately before "Why Switch". An incident in Discord: someone reports checkout failing, an agent opens an incident channel, pulls the error rate and finds the deploy behind it, with a second agent doing the charting. One collapsible block per app, Discord open and Slack and Mattermost waiting, so adding the next recording is pasting one URL.

How the video is hosted, and why it matters

The recording is a GitHub attachment, not a file in this repository. Nothing was committed.

That was worth establishing rather than assuming, because most of the obvious ways do not work. Checked against the rendered page on a branch, not from memory:

In a README	Result
<video> tag	stripped to a link
Link to an .mp4 committed here	plain link
blob/…?raw=true	plain link
Bare user-attachments URL on its own line	plays

It also plays inside <details> and inside a centered <div>, which is what lets the section hold one block per app without running long.

The earlier revision of this branch committed an 11 MB .mp4 and a poster image. Both are gone, and the branch was rewritten so the blobs are not in its history — three recordings would otherwise have put roughly 33 MB into the repository permanently, paid by everyone who clones. A comment above the section says so, so the next person reaches for an attachment instead.

Worth a look before merging

• The recording shows real names. Two colleagues' first names appear in the channel, and the left rail lists the other Discord servers the recorder belongs to. Nothing sensitive to Switch, but a README is public and permanent.
• I have not watched the video, only sampled frames from it. The description is written from those.