docs: add static before/after image to README

Add a before/after PNG showing try/catch vs neverthrow's typed
Result pattern with syntax highlighting. 75KB image.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: oferlmntr

README.md

@@ -6,6 +6,8 @@
 
 Encode failure into your program.
 
+![Demo](assets/demo.png)
+
 This package contains a `Result` type that represents either success (`Ok`) or failure (`Err`).
 
 For asynchronous tasks, `neverthrow` offers a `ResultAsync` class which wraps a `Promise<Result<T, E>>` and gives you the same level of expressivity and control as a regular `Result<T, E>`.