Index.html needs one more meta for a perfectable Lighthouse score

[petecarapetyan]

Everything required to get a Lighthouse score can now be furnished by my own site.webmanifest except this line that is required in the generated index.html

<meta name="theme-color" content="#ffffff"/>

Context: next branch of the rocket-51 preset

Workaround: npm run build then go into _site/index.html and add this tag before deploying