docs: add CODE_OF_CONDUCT and CONTRIBUTING guidelines

[kevinccbsg]

This pull request adds important documentation to the project by introducing a Code of Conduct and a Contributing Guide, and also updates the README.md for clarity and accuracy. These changes help set clear expectations for community behavior, contribution workflow, and usage instructions, making it easier for new contributors to get started and for users to correctly integrate the library.

New documentation:

• Added a CODE_OF_CONDUCT.md file based on Contributor Covenant 3.0, outlining community expectations, reporting procedures, and enforcement for a safe and inclusive environment.
• Added a CONTRIBUTING.md file with guidelines on how to contribute, set up the project, run tests, submit pull requests, and follow the code of conduct.

Improvements to usage instructions:

• Updated the README.md to use consistent double-quote imports in code examples, improving clarity for users integrating the library. [1] [2]
• Corrected the CLI command for initializing the mock service worker from npx twd-mock to npx twd-js, ensuring users follow the correct setup process.
• Minor formatting and whitespace adjustments in the README.md for readability and consistency. [1] [2]

These updates enhance the project's accessibility, usability, and community standards.

This closes #27