- Log into your Ghost control panel and open the ===Code injection=== page
- Add the required css and js references to your "Blog Header" and "Blog Footer", respectively, from your favorite CDN (or just use CloudFlare)
- You can then add code blocks to your editor as follows:
Type "/m" to insert a markdown block
And type ```javascript to add a block of javascript, or ```bash to highlight your bash scripts etc.
Make sure to put the starting and ending Prism markdown around your code on their own lines. If you put them on the same line as your code, it won't work properly. ~Eric Mathison
The end result looks like this:
<script>
$("pre").addClass("line-numbers");
</script>
Related: Make Prism.js Show Line Numbers by Default Using jQuery
There are also some much better written tutorials on the topic: