Display strapline explaining nature of Reasonator

[Andy Mabbett]

On pages - for example https://tools.wmflabs.org/reasonator/?q=Q504 - it would be sensible to have a strapline, below the Reasonator logo but above the H1 ("Émile Zola (Q504)") line, saying something like "Displaying public domain data from Wikidata", so that the site's nature is apparent to first-time visitors.