feat: Update README, setup.py, and suno/suno.py files
- Add a custom mode example to the README.md file, including code snippet and explanation
- Update the version number from "0.2.4" to "0.3.0" in setup.py
- Update the author's email address, project URL for bug reports, package dependencies, and Python version classifiers in setup.py
- Import the `random` module and add a list of music genres called `MUSIC_GENRE_LIST` in suno/suno.py
- Modify the `get_songs` method to use a random genre tag if not specified in suno/suno.py
- Modify the `save_songs` method to use the default output directory "./output" in suno/suno.py
Signed-off-by: yihong0618 <[email protected]>
