Update README with improved documentation and examples

[codegen-sh]

This PR updates the README.md file with several improvements:

Changes

• Enhanced the main heading to highlight the natural, intuitive API
• Added a new "Features" section to showcase key capabilities
• Updated CLI examples to include the required PATH parameter for codegen create command
• Added a more comprehensive code example in the Usage section
• Improved formatting and fixed capitalization of TypeScript and JavaScript
• Added links to API Reference and CLI Commands in the Resources section
• Expanded the code example to show more practical use cases
• Improved overall formatting and readability

These changes make the README more informative and better showcase Codegen's capabilities to new users.