docs: clarify sponsorship tiers, payment terms, and editorial policy

- Link awesome-python.com in sponsor descriptions
- Add 120-character limit for sponsor descriptions
- Reword Link Sponsor tier to clarify entry format
- Replace month-to-month wording with flexible term details
- Add payment methods (ACH/wire, PayPal)
- Add editorial reserve clause for sponsor content

Co-Authored-By: Claude <noreply@anthropic.com>