Where should I add defer attribute in Shopify script for parallel fetching?

[chrisinlondon]

This experiment adds a defer attribute to render-blocking scripts, causing the browser to fetch them in parallel while showing the page. Deferred scripts still execute in the order they are defined in source.

Example implementation: <script src="/cdn/shop/t/2/assets/crucial-commerce-page-speed.js?v=182156177923500543921693551231" defer></script>

ASSETS/INSTRUCTIONS:

/cdn/shop/t/2/assets/crucial-commerce-page-speed.js?v=182156177923500543921693551231

can someone tell me where i add the above code in my shopify theme for this to work