docs: Fix .sr-only docs

Author: jackdomleo7

src/docs/scss_modules.mdx

@@ -21,5 +21,5 @@ This module contains 2 classes that can be used to hide elements visually but ke
 ```html
 <button class="icon-only"><span class="sr-only">Close</span> &times;</button>
 
-<button class="sr-only--focusable">Skip to main content</button>
+<button class="sr-only sr-only--focusable">Skip to main content</button>
 ```