Layout documentation needs better escaping

[kornysietsma]

The documentation in https://github.com/jekyll/jekyll-archives/blob/master/docs/layouts.md has no escaping of liquid tags.

This leads to very confusing output on the page at https://jekyll.github.io/jekyll-archives/layouts/ where sample layouts look like:

<h1>Archive of posts with  'Layouts'</h1>
<ul class="posts">
  
</ul>

instead of having the actual liquid tags needed.

[ashmaroli]

Thank you for reporting this @kornysietsma