Add breadcrumbs at the top so you know where you are

(It has been suggested that we change the URL structure, however I split pages up and change their nesting from time to time and don't want to break old URLs, so I'm happy with our existing two-level (`/project/page`) system of URLs. Breadcrumbs should help people navigate though 👍 )

The issue concerns the website's shared navigation and its existing two-level /project/page URL structure. Start by locating the page layout or navigation entry point that can render breadcrumbs without changing old URLs. Done means pages show useful breadcrumbs for their project and page nesting while existing URLs continue to work.

Scritto dal modello di indicizzazione a partire dal testo della issue.