docs: align strategy docs with botasaurus-first auto fallback

[gildesmarais]

Summary

• update Ruby gem docs to include botasaurus strategy coverage
• simplify high-level wording to JavaScript/browser-based extraction while keeping concrete strategy details in reference pages
• document CLI default fallback order: faraday -> botasaurus -> browserless
• add BOTASAURUS_SCRAPER_URL guidance in strategy/CLI/troubleshooting docs

Why

This docs update tracks the Botasaurus strategy introduction in html2rss core:

• feat(strategy): add Botasaurus strategy html2rss#357

and new default auto strategy:

• feat: make strategy optional + default to automatic selection & raise on empty feed html2rss#358

Validation

• npm run -s build