Update README with new API methods and improve formatting

[tsjdev-apps]

Expanded the README to document additional API methods for geolocation and air pollution data. Improved formatting for badges, links, and sample image. Updated the sample screenshot.
This pull request introduces significant updates to the OpenWeatherMapSharp library, including new features, documentation improvements, and changes to the project configuration. The most important changes include the addition of air pollution endpoints, updates to the README for better clarity and formatting, and modifications to the project file to enable package generation and include new metadata.

New Features:

• Added new methods to support air pollution data retrieval:
  • GetAirPolutionAsync: Retrieves current air pollution data for a specific location. [1] [2]
  • GetAirPolutionForecastAsync: Retrieves forecasted air pollution data for the coming days for a specific location. [1] [2]
  • GetAirPolutionHistoryAsync: Retrieves historical air pollution data for a specific location and time range. [1] [2]

Documentation Improvements:

• Enhanced the README.md file:
  • Updated formatting for links and badges to improve readability. [1] [2]
  • Revised method descriptions for clarity and consistency. [1] [2] [3] [4] [5]
  • Added detailed examples of new methods for air pollution and geolocation queries. [1] [2]

Project Configuration Updates:

• Updated OpenWeatherMapSharp.csproj:
  • Enabled package generation during build (GeneratePackageOnBuild set to True).
  • Bumped the version to 4.0.0 to reflect the addition of new features.
  • Included README.md in the NuGet package metadata.

These changes collectively enhance the library's functionality, usability, and maintainability.