If you are familiar to HTML, you should be able to implement this easily. You would simply edit the /partial header .hbs file associated with the post.hbs (or similar name). You can find this by editing the post.hbs (or similar name) and looking for something like…
{{>post-head}}
…this is just an example. It should be the first line or thereabouts.
Please keep in mind that themes vary, however, these guys are highly disciplined and they all follow a similar pattern of development.
It could be interesting to have it included into the Publii GUI, but that is up to the coders. I seems like it would be a relatively simple add. Options on the web change quickly. For example, there are a lot of new social media sites and apps available and people are moving away from Facebook and Twitter by the millions every day. I imagine that keeping up with the options available is more than a fulltime job for somebody.
