Add clarification for --enable-framework in macOS build instructions

[minikids]

This PR updates the macOS build instructions to explain what the --enable-framework option does.
The note clarifies that this flag builds Python as a macOS framework, which is required for GUI modules like tkinter to function correctly.

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📚 Documentation preview 📚: https://cpython-devguide--1646.org.readthedocs.build/

[python-cla-bot]

All commit authors signed the Contributor License Agreement.

[hugovk]

Suggested change

	Without ``--enable-framework``, you still get a working command-line
	``python3``, but certain macOS-specific integrations (GUI event loops,
	app embedding, etc.) will not work.
	Without ``--enable-framework``, you still get a working command-line
	``python3``, but certain macOS-specific integrations (such as GUI event
	loops and app embedding) will not work.

[hugovk]

cc @ned-deily

[ezio-melotti]

LGTM (with Hugo's suggestion).

[ned-deily]

Thanks for the PR but the section that it adds the clarification to refers to the steps in cross-building Python targeted for iOS and iOS simulators, not for Pythons running on macOS. The --enable-framework option is needed for execution on non-MacOS Apple platforms and has nothing to do with gui libraries etc which would only apply to builds targeted for macOS.