docs: add reference to frameworks documentation

[sambarnes]

docs: add reference to frameworks documentation

Summary

This PR addresses GitHub issue #93 by adding a reference to the correct OpenRouter frameworks documentation in the README.md file. The issue reported that users were encountering a "page not found" error when trying to access frameworks documentation from the OpenRouter website.

Root Cause: The broken link https://openrouter.ai/docs/community/frameworks returns a 404 error, while the correct URL is https://openrouter.ai/docs/community/frameworks-overview.

Solution: Added a helpful reference to the correct frameworks documentation URL in the README.md file's "Supported models" section, making it easier for users to find integration guides for popular frameworks and SDKs.

Review & Testing Checklist for Human

• Verify the frameworks documentation URL (https://openrouter.ai/docs/community/frameworks-overview) loads correctly and shows relevant content
• Check that the placement of the new documentation reference in the README makes sense and flows well with the existing content
• Confirm this addresses the user's need expressed in GitHub issue [bug]: page not found #93

---

Diagram

%%{ init : { "theme" : "default" }}%%
graph TD
    Issue["GitHub Issue #93<br/>page not found"]
    README["README.md<br/>Supported models section"]:::major-edit
    BrokenURL["https://openrouter.ai/docs/<br/>community/frameworks<br/>(404 Error)"]:::context
    CorrectURL["https://openrouter.ai/docs/<br/>community/frameworks-overview<br/>(Working)"]:::context
    
    Issue --> README
    README --> CorrectURL
    BrokenURL -.-> CorrectURL
    
    subgraph Legend
        L1[Major Edit]:::major-edit
        L2[Minor Edit]:::minor-edit  
        L3[Context/No Edit]:::context
    end
    
    classDef major-edit fill:#90EE90
    classDef minor-edit fill:#87CEEB
    classDef context fill:#FFFFFF

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Notes

• The change is minimal and low-risk - only adding a documentation reference
• The frameworks documentation page contains integration guides for OpenAI SDK, LangChain, PydanticAI, Vercel AI SDK, and Mastra
• This helps users discover the frameworks documentation they need without encountering broken links
• Link to Devin run: https://app.devin.ai/sessions/58b26021f90549489e6c90ce51933b7f
• Requested by: @sambarnes

[devin-ai-integration]

Original prompt from sam:

SYSTEM:
=== BEGIN THREAD HISTORY ===
GitHub (U05HMK4U3D1): 

[OpenRouterTeam/ai-sdk-provider] Issue opened by Boby900

sam (U06DJ8YS066): @Devin would you mind investigating this bug report? I think we have a broken link
=== END THREAD HISTORY ===

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