docs: add TweetClaw import example

[kriptoburak]

Summary

• update the import section heading so it covers both broad registries and focused skill repos
• add TweetClaw's packaged OpenClaw skill as a focused GitHub source users can paste into SkillNote

Validation

• bash scripts/check-readme-links.sh
• git diff --check
• direct check: https://github.com/Xquik-dev/tweetclaw/tree/master/skills/tweetclaw returns 200

Note: generic npx markdown-link-check README.md still reports pre-existing target-owned failures for npm package pages returning 403 and the documented http://localhost:3000 local URL. The new TweetClaw link passes in that check.

[kriptoburak]

Optional visibility note: if this is useful and you merge it after checks pass, feel free to share the PR on X/Twitter and tag or mention the X account name burakbayir. I can repost it to my 24k followers so more developers and power users can discover this repo.