📝 Add user-friendly documentation for Bizao adapter

✨ Context

EasySwitch includes an integration for Bizao (easyswitch.integrators.bizao).
However, the documentation is currently too technical and may not be easily understandable for developers who are new to EasySwitch or payment aggregators.

We want to provide a clear, pedagogical, and comprehensive guide for using the Bizao adapter.

📌 What needs to be done

• Create a dedicated documentation page for BizaoAdapter.
• Explain step by step how to configure and use it:
  • How to set up credentials (api_key, api_secret, base_url, etc.)
  • Sandbox vs Production environments
  • Required fields for transactions
  • Common pitfalls & error handling
• Add examples (Python code snippets) for:
  • Sending a payment
  • Checking transaction status
  • Handling webhooks (validation & parsing)
  • Refunding a transaction
• Provide practical examples (e.g., integrating Bizao for mobile money payments).
• Ensure the documentation is simple, user-friendly, and easy to follow.

✅ Expected outcome

• A dedicated, user-friendly documentation page in the EasySwitch docs (docs/integrators/bizao.md).
• Clear examples and explanations that reduce onboarding friction.
• Helpful for both beginners and experienced developers.

💡 Notes

• Look at the BaseAdapter documentation as a model.
• Bonus: include a visual diagram showing the Bizao payment workflow in EasySwitch.

🎉 Why this matters

Bizao is a popular aggregator for mobile money and digital payments in Africa.
Improving its documentation will make EasySwitch more accessible to local developers, and foster wider adoption.

This issue is Hacktoberfest-friendly 🚀