Clarify baseline for new interpreter

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📚 Documentation preview 📚: https://cpython-previews--129972.org.readthedocs.build/

[hugovk]

Would you like to include this in the release highlights?

If so, would you like to suggest a brief summary?

Perhaps something like:

- A [new type of interpreter](https://docs.python.org/3.14/whatsnew/3.14.html#whatsnew314-tail-call). For certain newer compilers, this interpreter provides significantly better performance. Opt-in for now, requires building from source.

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@hugovk yes please, that snippet seems good to me!