docs: add OpenClaw plugin bridge example

[kriptoburak]

Summary

• Add a README section for using OpenClaw-native plugins through this MCP bridge.
• Document TweetClaw as a concrete X/Twitter automation example for bridged OpenClaw sessions.
• Update the MCP Specification link to the current official specification URL.

Validation

• Searched the repo and all open and closed issues and PRs for TweetClaw, Xquik, @xquik/tweetclaw, Xquik-dev/tweetclaw, npmjs.com/package/@xquik/tweetclaw, and x-twitter-scraper. No duplicates found.
• Checked README external and local links after stripping code examples: 16 external links, 8 local links, 0 failures.
• git diff --check
• npm run lint
• npm run typecheck
• npm run test:run
• npm run build
• npm view @xquik/tweetclaw version --silent returned 1.6.31

[freema]

Thanks for the contribution, but this project doesn't endorse or document third-party commercial plugins in the README. Closing.