📝 Add docs for virtual environments and environment variables, update contributing

[tiangolo]

📝 Add docs for virtual environments and environment variables, update contributing

[github-actions[bot]]

📝 Docs preview for commit 68134ae1a2058aa9f39f69ed6b9fb2c860ea16b9 at: https://030c6c42.sqlmodel.pages.dev

Modified Pages

• https://030c6c42.sqlmodel.pages.dev/
• https://030c6c42.sqlmodel.pages.dev/contributing/
• https://030c6c42.sqlmodel.pages.dev/databases/
• https://030c6c42.sqlmodel.pages.dev/environment-variables/
• https://030c6c42.sqlmodel.pages.dev/install/
• https://030c6c42.sqlmodel.pages.dev/tutorial/
• https://030c6c42.sqlmodel.pages.dev/tutorial/fastapi/simple-hero-api/
• https://030c6c42.sqlmodel.pages.dev/tutorial/fastapi/tests/
• https://030c6c42.sqlmodel.pages.dev/virtual-environments/