Add Detailed Documentation for pip-upgrader

[bonaventureogeto]

This pull request enhances the documentation for the pip-upgrader project by adding comprehensive details on its usage, installation, and features. The updated documentation includes:

• A clear overview of the package's purpose and key features.
• Installation instructions, including notes on dependencies.
• Detailed usage examples with explanations of command-line arguments.
• Instructions on using pip-upgrader with setup.py and managing multiple requirements files.
• A new FAQ section to address common questions.
• Contribution guidelines for those interested in improving the project.
• Integration of the quick preview GIF to visually demonstrate the tool's functionality.

These changes are designed to improve the user experience, making it easier for new and existing users to understand and effectively use pip-upgrader. The updated documentation also encourages community contributions by providing clear guidelines.

This PR addresses the issues discussed in Issue #54, Issue #55, and Issue #56.

The project is currently unmaintained, but these documentation improvements will make it easier for the community to use and potentially maintain the tool in the future.