[3.13] gh-132898: Add a note in multiprocessing.Process docs about creating a process in a REPL (GH-137118)

[miss-islington]

• Reword, expand, and clarify the limitation, highlighting the REPL case.
• Mention in the high level Process description.
• added a pointer to the GH issue from the doc note

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(cherry picked from commit 4e40f2b)

Co-authored-by: Duprat [email protected]
Co-authored-by: Gregory P. Smith [email protected]

• Issue: REPL: AttributeError: module __mp_main__ has no attribute is_prime in ProcessPoolExecutor example #132898

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📚 Documentation preview 📚: https://cpython-previews--137155.org.readthedocs.build/

[brianschubert]

docs build failed with undefined label: 'multiprocessing-programming-spawn'. That label was added in #128173, which wasn't backported to 3.13. I opened #137156 to add the labels to the 3.13 docs

[gpshead]

Thanks! Looks like our CI docs build caught that but isn't configured as a blocking requirement.