Add "last updated" date to the bottom of pages in the docs

The speed the team is putting out new features and improvements is really impressive! However, sometimes the docs have a hard time keeping up. A date tag at the bottom of each page would be very helpful when comparing depreciated information. For example, the [Build a User Management App with SvelteKit Tutorial]( uses auth-helpers-sveltekit and makes no mention of the new @supabase/ssr package.