Add Inter-UI fonts explicitly

These fonts are referenced in primer-marketing but are not found in the node module.

This is necessary until we upgrade Primer, where the fonts are already bundled: https://github.com/primer/css/tree/master/fonts

Author: talsafran

assets/css/index.scss

@@ -1,9 +1,13 @@
 ---
 ---
 
+// The Inter-UI-* fonts referenced in primer-marketing are located here, until we upgrade to the new Primer.
+$marketing-font-path: "/assets/fonts/";
+
 @import "primer-core/index.scss";
 @import "primer-marketing/index.scss";
 @import "toc.scss";
 @import "custom.scss";
 @import "covers.scss";
 @import "anchor.scss";
+