docs(render_com): update instructions

[MickL]

🔗 Linked issue

https://github.com/unjs/nitro/issues/2535

❓ Type of change

• [x] 📖 Documentation (updates to the documentation, readme, or JSdoc annotations)
• [ ] 🐞 Bug fix (a non-breaking change that fixes an issue)
• [ ] 👌 Enhancement (improving an existing functionality like performance)
• [ ] ✨ New feature (a non-breaking change that adds functionality)
• [ ] 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• [ ] ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

There is no need for the render.com preset. I updated the steps to the latest render.com UI and I also added Bun as an alternative runtime which render.com supports

📝 Checklist

• [x] I have linked an issue or discussion.
• [x] I have updated the documentation accordingly.