Docs: Update "Installing Python modules"

[hugovk]

• distutils is gone, we don't need to mention it or the mailing list it inspired (and is now closed)
• The wheel format is no longer the bright new hope, it's widely adopted
• Remove some detail about Python 3.3/3.4 that is no longer relevant
• Use program directive for commands
• Use shell highlighting by default
• Sentence case header
• A bit of copyediting
• Update examples

---

📚 Documentation preview 📚: https://cpython-previews--146249.org.readthedocs.build/