docs: add Kiro support, drop npm badge

[tqtensor]

Summary

• Adds Kiro (.kiro/settings/mcp.json) to the existing Cursor / Claude Desktop / Windsurf table; renames the heading to "Cursor, Claude Desktop, Kiro & Windsurf". Mirrors the substantive part of the upstream Kiro PR while keeping this fork's section structure.
• Drops the npm version badge — this fork installs from the GitHub repo, not from @perplexity-ai/mcp-server, so the badge was misleading.
• Deliberately skips upstream's "Install in Cursor / VS Code / Kiro" install badges (they hardcode @perplexity-ai/mcp-server + PERPLEXITY_API_KEY and would launch the upstream server) and skips the upstream consolidation that folds VS Code into the mcpServers table (this fork keeps a separate VS Code section documenting the servers / type: stdio schema).

Closes #1.

Test plan

• README.md renders correctly on GitHub: heading reads "Cursor, Claude Desktop, Kiro & Windsurf", table includes Kiro, no npm badge near the title.
• VS Code section is still present below with the servers / type: stdio JSON unchanged.
• After merging, issue Upstream sync: 5 new commit(s) from perplexityai/modelcontextprotocol #1 auto-closes.
• Next run of .github/workflows/upstream-sync.yml reports main is no longer behind perplexityai/modelcontextprotocol@main for substantive content (the workflow may still flag pure formatting/badges; if so, that's expected and can be ignored).