Use the disc list style type

Previously, it was the `circle` list style type, but it was determined
that the `disc` list style type is in many ways a better match for Rust.

Author: camelid

src/styles/app.scss

@@ -186,7 +186,7 @@ section {
 }
 
 ul {
-  list-style: circle;
+  list-style: disc;
   padding-left: 1.5em;
 }