This PR enhances the dataset card for `TestEval-extend` by:
- Adding `task_categories: ['text-generation']` and relevant `tags` (`code-generation`, `unit-test-generation`, `diffusion-llm`) to the metadata for improved discoverability.
- Including a link to the official GitHub repository: `https://github.com/wellbeingyang/DLM4UTG-open`.
- Adding an "Overview" section to describe the dataset's purpose and features.
- Adding a "Sample Usage" section, detailing installation steps and the command to reproduce the main results, directly sourced from the GitHub README. The `tar` command for Maven has been corrected for internal consistency with the `wget` and `export` commands.
