title: Change favicon and title consistently on blogdown site
body: <p>I am new to blogdown and haven't done any other work with website creation so apologies if this stuff seems really beginner level!</p>
  
  <p>I have defined the title of my blog in <code>config.toml</code> and I've saved my favicon image in my <code>static</code> directory as <code>favicon.ico</code>. When my blog is opened, the tab shows the right icon and title. Great!</p>
  
  <p>The problem is that when I copy a link to a post in a way that shows a preview, sometimes the favicon and title will default to the theme's standard ones - so simply 'Title' and the <a href="https://github.com/htr3n/hyde-hyde" rel="nofollow noreferrer">hyde-hyde</a> favicon. The behaviour varies a little - for e.g. in slack, both these things are back to the example, whereas in Whatsapp, it seems to keep my post's title but not the favicon. </p>
  
  <p>I've tried using <a href="https://stackoverflow.com/a/48491948/8506921">this answer</a>, which is how I got the favicon working in my tab, but I still have the issue with the post previews. I haven't been able to work out the second option as I don't know where the  element is in the hyde-hyde theme. </p>
  
  <p>Can anybody tell me how to fix this across platforms?</p>
  
  <p>I'm not sure how one would make a reproducible example of this, but if there is specific stuff (like code from certain files or more info) that would be useful let me know and I'll provide it.</p>