Adding Open Graph meta properties

[bart-kneepkens]

To make my landing page shareable, I've added a few og: tags to my head.xml . This worked perfectly, and I was wondering, would such an addition to this repository be appreciated? If so, I'd be happy to create a PR.

og:title, og:image, and og:description can all be dynamically set using {{ site.property }}. Not sure if what property we can use to dynamically set og:url.

[emilbaehr]

Hi there! Really good idea, thanks.
Go ahead, appreciate it.