Changes in depcurfew 1.5.2

Documentation site

• Every page of https://depcurfew.github.io has its own description, names its address as the canonical one and has Open Graph tags, so search results and shared links show its title and what it is about. The start page is titled "depcurfew · Supply-chain security policy for package managers".
• The site has robots.txt, sitemap.xml with the pages of the current version, and a page for addresses that do not exist. The pages of earlier versions stay readable but are marked noindex, so search engines list the current documentation.
• The homepage of the npm package is the documentation site instead of the README on GitHub.