Docs: add note and advice about .disabled and keyboard focus

/cc @cvrebert

docs/components/buttons.md

@@ -125,7 +125,7 @@ As `<a>` elements don't support the `disabled` attribute, you must add the `.dis
 {% callout warning %}
 #### Link functionality caveat
 
-This class uses `pointer-events: none` to try to disable the link functionality of `<a>`s, but that CSS property is not yet standardized and isn't fully supported in Opera 18 and below, or in Internet Explorer 11\. In addition, even in browsers that do support `pointer-events: none`, keyboard navigation remains unaffected, meaning that sighted keyboard users and users of assistive technologies will still be able to activate these links. So to be safe, use custom JavaScript to disable such links.
+The `.disabled` class uses `pointer-events: none` to try to disable the link functionality of `<a>`s, but that CSS property is not yet standardized and isn't fully supported in Opera 18 and below, or in Internet Explorer 11\. In addition, even in browsers that do support `pointer-events: none`, keyboard navigation remains unaffected, meaning that sighted keyboard users and users of assistive technologies will still be able to activate these links. So to be safe, add a `tabindex="-1"` attribute on these links (to prevent them from receiving keyboard focus) and use custom JavaScript to disable their functionality.
 {% endcallout %}
 
 ## Button plugin