docs(sarvam-mcp): correct stale tool and installation references

[amitkarpe]

Summary

This small documentation-only change aligns the sarvam-mcp skill with the
current public sarvamai/sarvam-mcp source.

• Removes sarvam_code_search_docs / search_docs, which is not registered
  by the current server.
• Keeps the registered sarvam_code_pricing guidance.
• Replaces the dead docs/INSTALLATION.md link (HTTP 404) with the reachable
  upstream README, which contains setup and configuration guidance.

Closes #3.

Validation

• git diff --check
• Confirmed no stale search_docs guidance remains in the three edited files.
• Confirmed https://github.com/sarvamai/sarvam-mcp#readme returns HTTP 200.
• Reviewed current public open issues and PR titles; no matching duplicate was
  found.
• Ran a fresh read-only skill forward test: it selected
  sarvam_code_pricing and sarvam_code_api_reference and did not name a
  nonexistent search tool.

No runtime behavior, dependencies, credentials, or API calls are changed.

[mangeshraut712]

Heads-up: opened #5 which includes the same stale search_docs / install-link fixes from this draft, plus aligning the chat skill to sarvam-105b for coding agents. Happy to coordinate — maintainers can take either PR.