[DOC] Added examples for temporal_train_test_split docstring

[JonathanBechtel]

Reference Issues/PRs

#4154

What does this implement/fix? Explain your changes.

I added better documentation for the temporal_train_test_split function, as it lacks examples

Does your contribution introduce a new dependency? If yes, which one?

No

What should a reviewer concentrate their feedback on?

Make sure examples are relevant and accurate

Did you add any tests for the change?

This is just a doc string fix, so no tests were added

Any other comments?

No

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[fkiraly]

typo - _make_panel is from sktime.utils._testing.panel

[JonathanBechtel]

@fkiraly Thank you, fixed.