docs: add TweetClaw plugin option

[kriptoburak]

Summary

• Add a README note for using TweetClaw as an optional OpenClaw plugin path beside ClawSync's built-in X integration
• Keep ClawSync's X Developer Portal setup as the default path for Convex-managed credentials
• Document common X/Twitter workflows and credential separation for Xquik configuration

Validation

• git diff --check
• Added-line dash and sensitive-string scans
• TweetClaw GitHub link returned HTTP 200
• ClawSync GitHub link returned HTTP 200
• npm view @xquik/tweetclaw version --json returned 1.6.31

No runtime tests were run because this is a README-only documentation change.