PEP 747: Add new "How to Teach This" section. Address other feedback.

[davidfstr]

• Change is either:
  • [x] To a Draft PEP
  • [ ] To an Accepted or Final PEP, with Steering Council approval
  • [ ] To fix an editorial issue (markup, typo, link, header, etc)
• [x] PR title prefixed with PEP number (e.g. PEP 123: Summary of changes)

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📚 Documentation preview 📚: https://pep-previews--3849.org.readthedocs.build/

[davidfstr]

(All suggested changes applied)