Document correct class prefix in CSS comments

client/scss/core.scss

@@ -71,7 +71,7 @@ These are base styles for bare HTML elements.
 
 /* COMPONENTS
 These are classes for components.
-* These classes (unless legacy) are prefixed with `.c-`.
+* These classes (unless legacy) are prefixed with `.w-`.
 * React component styles live in the same folders as their React components,
   which is the preferred pattern over housing them in the scss folder.
 */