docs(readme): add deepseek in support models

[sl-gn]

📝 Change Type

Please select the type of change this PR introduces (choose one or more):

• feat: New feature.
• fix: Bug fix.
• [✅] docs: Documentation only changes.
• [✅] refactor: A code change that neither fixes a bug nor adds a feature.
• perf: Performance improvement.
• test: Adding missing tests or correcting existing tests.
• chore: Maintenance tasks (e.g., updating dependencies).

💡 Description

add deepseek in support models

Key Changes

1. update readme file, add deepseek in support models
2. add models in backend model list

🔗 Related Issues