[DOC] Updated documentation on TimeSeriesDataSet.predict_mode

[madprogramer]

Description

Documentation PR.
Clarifies use of predict_mode for TimeSeriesDataSet.

Checklist

• Linked issues (if existing)
• Amended changelog for large changes (and added myself there as contributor)
• Added/modified tests
• Used pre-commit hooks when committing to ensure that code is compliant with hooks. Install hooks with pre-commit install.
  To run hooks independent of commit, execute pre-commit run --all-files

Make sure to have fun coding!

[madprogramer]

I believe this is also connected to the TimeSeriesDataSet.from_dataset method.

See also use in The TFT tutorial.