Avoid over-linking #1293

[nedbat]

Summarizing and codifying the advice discussed in https://github.com/python/docs-community/issues/52

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📚 Documentation preview 📚: https://cpython-devguide--1294.org.readthedocs.build/

[nedbat]

Changes made, and I added another rule: no links in section titles.

[hugovk]

Thanks!

[willingc]

Thanks @nedbat