docs: add animated demo GIF to README

[ofershap]

Summary

• Adds an animated before/after GIF showing try/catch with unknown errors vs neverthrow's typed Result with .match()
• Placed right after the description heading for immediate visual impact
• GIF stored in assets/demo.gif (~1 MB)

The animation was generated with Remotion using the Catppuccin Mocha color scheme.

Preview

The GIF shows:

• Left panel (Before): Traditional try/catch where e is unknown and error source is ambiguous
• Right panel (After): neverthrow's andThen chain with fully typed error handling via .match()

Motivation

neverthrow's README is comprehensive but entirely text-based. A visual demo at the top helps new visitors immediately understand the value proposition before diving into the API docs.

Made with Cursor

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[supermacro]

Hey @ofershap this is really cool! Thank you. I wonder, though, if it would make more sense to just show the before / after as a static image such as this:

If we can have it with simple syntax highlighting that'd be awesome too.

[ofershap]

Good call — swapped the animated GIF for a static PNG (75KB). It shows both panels side-by-side with syntax highlighting. Let me know if you'd like any tweaks to the colors or layout!