Extend Django.py Cheat Sheet: Incorporate Unit Testing and Coverage Information

This commit enhances the existing Django.py cheat sheet by integrating guidance on unit testing and coverage analysis. The update includes detailed instructions on writing unit tests within Django applications, setting up test fixtures, executing tests locally, and leveraging coverage tools for assessing code coverage.

Changes:
- Added comprehensive instructions on writing unit tests for Django applications.
- Included guidance on setting up test fixtures and organizing test files.
- Provided commands and examples for running tests locally using Django's testing framework.
- Introduced information on using test coverage tools like `coverage.py` to assess code coverage.
- Enhanced the documentation to ensure clarity and completeness.

This update aims to empower developers with the necessary knowledge and resources to ensure the robustness and reliability of their Django projects through effective testing and coverage analysis.