You can edit the customer account page in your theme templates, it's usually called something like customers/account.liquid.
You can add the code / referral link(s) you want to in that file.
Founder of Speed Boostr (Shopify optimization experts, theme customization, custom app development). Creator of Shopify Analyzer (first performance analysis tool for Shopify sites, free for the Shopify community). Creator of Order Automator (auto tag orders and customers + auto fulfill orders + email notifications). Creator of Theme Scientist (A/B testing app) and Tip Jar (add a tip button to your store).