First load of your page took a very long time for me. I think you'll have a very high bounce rate until you get your static page load times under control.
According to the first site testing tool I found (https://www.dotcom-tools.com/website-speed-test.aspx), there's a clear delay when accessing from outside Europe or Canada. Less than 2s to Frankfurt and London, but 5-6 for the US and 11+ to Australia.
I looked into it.
Gzip compression was off, even though it was configured in nginx.
Highlightjs was included in my main javascript, while I only need it for the instructions to highlight some html/js/ruby/php. It's a whopping 100kb by itself.
I moved this to the instructions page, and I'm using cloudfront now as a CDN.