@docusaurus/plugin-sitemap ↔ docu plugin to gen sitemap for site for SEO Web Crawler | pack with classic preset
@docusaurus/plugin-sitemap incl with preset-classic - no need to install!
changefreq
to set frequency for crawler to re-index "always", "hourly", "daily", "weekly", "monthly", "yearly", "never"
@docusaurus/plugin-sitemap will not run in dev mode - only active on prod (despite build output still being made for dev mode - just to annoy us?)