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MINOR: [Documentation][Python] Minor tweaks to docs around IPC messages (#35880)

### Rationale for this change

@ jorisvandenbossche pointed out that the docstring for RecordBatch.serialize might not be clear enough and that users may be surprised to find out a Schema isn't included. This PR makes that clearer and improves up related documentation.

### Are these changes tested?

Yes. I built the docs and verified the rendering was correct and I ran the changed example locally. I didn't --doctest-cython it because it looks like that hasn't been set up for this module.

### Are there any user-facing changes?

No, these are just docs improvements.

Lead-authored-by: Bryce Mecum <petridish@gmail.com>
Co-authored-by: Alenka Frim <AlenkaF@users.noreply.github.com>
Signed-off-by: AlenkaF <frim.alenka@gmail.com>