Update README.md to include comprehensive documentation for SDK usage and features

[srivishnua-lambdatest]

This pull request significantly updates the README.md file to provide comprehensive documentation for the LambdaTest Playwright SDK. The changes include an overview of the SDK, installation instructions, usage examples, advanced configuration options, and support information.

Documentation Enhancements:

• Updated the project title to "LambdaTest Playwright SDK" and added an introduction explaining its purpose for integrating LambdaTest's Smart UI testing with Playwright.
• Added detailed prerequisites, installation steps (via npm or yarn), and configuration instructions, including setting up environment variables and starting the Smart UI server.
• Included a basic usage example demonstrating how to use the smartuiSnapshot function in Playwright tests.

Advanced Usage and Options:

• Documented advanced configuration options for smartuiSnapshot, categorized into:
  • Element Selection Options (e.g., ignoreElements, captureElements)
  • Viewport and Display Options (e.g., viewport, deviceScaleFactor)
  • Image Quality Options (e.g., quality, format)
  • Region Control Options (e.g., clip, mask, overlay)
  • Annotation Options (e.g., adding text annotations) (