docs: improve documentation clarity and usability across the project

- Update links for language options in the README
- Improve descriptions for the CLI tool's functionality
- Add support for customizing the number of context lines in diffs
- Clarify instructions for setting up the OpenAI API key
- Enhance the configuration section with clearer language
- Change section titles for consistency and clarity
- Update installation instructions for macOS and Windows
- Revise examples and explanations for better readability
- Correct minor grammatical errors throughout the document
- Add details about using different API services and models

Signed-off-by: appleboy <[email protected]>

Author: appleboy