Create a new guide for crawling features

[vdusek]

• We could create a new documentation guide for all crawling-related features we provide.
• The guide should include the following:
  • enqueu_links helper function,
  • Crawling limitations and controls:
    • EnqueueStrategy,
    • max_requests_per_crawl,
    • max_depth (or depth_limit) - to be added in #460.