Add video demo to `README.md`

[ai]

We need a video of using https://ai.github.io/keyux/ with:

1. Press Alt+B (or Cmd+B on Mac) a few times
2. Press Tabs twice to move focus to menu
3. Press → and ← to see key navigation inside focus group
4. Press a and b to show quick search inside menu
5. Press enter to show focus jump on next submenu
6. Press Esc to go back
7. Press l and i to select List1
8. Press Enter
9. Press v to click first button
10. Press ↓ to go to the next button
11. Press v to show local hotkeys
12. Press Esc

The video should:

• Be in h264/mp4 format without sound
• Do not contain browser frame, etc. It should have small dimensions as possible.
• Show what key was pressed
• Find a right timing to be dynamic but understandable

[uzurpastor]

Hello, while testing I found an issue that the ‘S’ key binding is being overridden to ‘s’ and the ‘Settings’ button is not focusing. I assume that capital letters are not being caught, at least for Firefox 128 and Chromium 126.

I am now trying to fix this problem in the lib source code (I'm not good in js)

[ai]

@uzurpastor fixed https://github.com/ai/keyux/commit/1149aa2f88290556a151cd59b8ac6f01e40c111c

[uzurpastor]

PR: #27